Glossary of Technical Theatre Terms – The Theatre Building

See also

Anatomy of a Theatre


ACOUSTIC SHELL
(also known as BAND SHELL or CHORAL SHELL). A hard smooth curved surface which is designed to reflect the sound from the stage towards the audience. Some venues have shells which can be removed / repositioned or flown out of view to change the acoustics of the venue for different types of event. 

ACT DROP
Victorian stretched framed and painted canvas. Used as a visual stimulation during scene changes, and to indicate that there was more to come (the end being indicated by the HOUSE TABS). There are believed to be only two operational today - an original one at Gaiety Theatre, Isle Of Man, and a 1996 reproduction at Her Majesty's Theatre, Ballarat, Victoria, Australia.
Term now used to refer to any front cloth or tabs lowered during intervals. Especially pantomime / musicals. 
In ballet, the act drop permitted pre-interval curtain calls to take place. 
Gaiety Theatre
Her Majesty's Theatre

ACT NUMBER INDICATOR
An indicator board visible to the audience on the proscenium arch of a theatre used for variety performances which showed the Act Number so the audience could tell who was on stage (after referring to their printed programme). 
One type of board used replaceable numbers which were replaced by hand, another type used a paper scroll containing the numbers which was advanced either mechanically or electrically. The most popular type used an array of light bulbs which were illuminated in patterns to depict the numbers. 

AISLE
A passage through seating.

ALCOVE
A semi-enclosed recess in the wall of the auditorium, sometimes for technical equipment, sometimes for a statue or other decorative element. 

AMPHITHEATRE
Circular or oval open-air theatre with a large raked seating area (often semi-circular) sloping down to the stage. Originates from ancient Rome where vast amphitheatres were built for spectator sports and games.

APRON
The Apron is a section of the stage floor which projects towards or into the auditorium. In proscenium theatres, it's the part of the stage in front of the house tabs, or in front of the proscenium arch, above the orchestra pit. Also known as Forestage.
If an apron stage extension is added to an existing traditional proscenium arch theatre, this often results in poor sight lines from seats that are higher in the auditorium, leading to audience members having to lean forward in an attempt to see.
German: vorbühne (literally, forestage).

ARENA
Form of stage where the audience are seated on at least two (normally three, or all four) sides of the whole acting area.
See END ON, THRUST, IN THE ROUND.

AUDITORIUM
The part of the theatre accommodating the audience during the performance. Sometimes known as the "house". From the Latin Audio - "I hear".
German: Zuschauerraum

BACKSTAGE
The part of the stage and theatre which is out of the sight of the audience. The service areas of the theatre, behind, beside or underneath the stage. Also refers to the personnel who work in the technical departments that work to create the performance, alongside the actors and musicians. 
German: Hinterbühne

BALCONY
(US) American term for the Circle - upper level in the auditorium.

BASTARD PROMPT CORNER
Used when the Prompt Corner is Stage Right instead of the usual Stage Left. This may be for architectural reasons in a theatre with no wing space Stage Left, or may be because of the layout of set pieces which obscure a view from Stage Left, or because the band is on Stage Left and the Deputy Stage Manager can't hear her/himself cueing!

BLACK BOX
A kind of flexible small studio theatre where the audience and actors are in the same room, surrounded by black tabs (curtains). Doesn't necessarily describe the audience layout, which can be easily reconfigured.The stage can be defined by a change of flooring (e.g. black dance floor), or a raised platform. If actors leave the stage, they do so through gaps in the curtains. 
A black box type of venue is easy to set up in non-theatre spaces, and can be found occupying hundreds of spaces around cities such as Edinburgh during their Fringe Festivals. 

BOX OFFICE
(UK) Part of the theatre front of house area where audience members can buy tickets. Most Box Offices are now computerised, and offer phone reservations. Some offer online (internet) bookings also. 
Also known as the Ticket Booth (USA). 
See also WILL CALL.

BRIDGE
1) A walkway, giving access to technical and service areas above the stage or auditorium, or linking fly-floors.
See also CATWALK.
2) A lighting position above the auditorium, commonly with a catwalk above it to access lighting equipment and electrical systems is known in Dutch as a Zaalbrug.
3) A section within a song which provides a break from the previous verse / chorus, to prepare for the final chorus or climax, and can also provide a contrast with the previous lyrical tone or style.

BRIDGE LIFT
An elevator which raises and lowers sections of the stage floor, usually by electrical or hydraulic means.

CABARET SEATING
Seating layout featuring round tables arranged with chairs positioned 2/3rds of the way around the tables so that they can all face a raised stage. There should be plenty of space around the tables to allow circulation of waiting staff.

CARPET CUT
Hinged trap running the width of the stage, as far downstage as is practical, to secure the front edge of a painted floor (stage)cloth, or carpet. The other three sides of the floor cloth were 'tacked' down to prevent it being a trip hazard. Large companies (e.g. The Royal Ballet) used to lay a floor cloth for each act. A stage-hand, with spade or shovel, worked round the floor cloth to 'up-end' the tacks that were holding the cloth down. It was then folded in such a way, that for the following show, it was set with the downstage edge ready to go into the Carpet Cut. The floor cloth was always put in the carpet cut first, then pulled out taut by the crew and re-tacked. (becoming obsolete term)

CATACOMBS
Originally an underground cemetary, with spaces for tombs, built by the ancient Romans. 
Most widely known now in reference to the tunnels and cellars underneath the Paris Opera House, in The Phantom of the Opera. The theatre by which the musical was inspired, the Palais Garnier, has an underground lake which inspired the original story of the Phantom of the Opera. 
Paris Opera / Palais Garnier at Theatrecrafts.com

CATWALK
An access walkway to equipment. Unlike a BRIDGE, not necessarily across a void.

CIRCLE
The balcony with tiered seating above the stalls in a traditional proscenium arch theatre. Also known as Dress Circle or Grand Circle. See also UPPER CIRCLE.

CLOAKROOM
Area near the entrance of a theatre (or other public venue) where visitors may leave their coats and bags, in exchange for a small fee. The cloakroom attendant provides a numbered ticket or token, a duplicate of which is kept with the coat / bag to identify it. 
US: Coat Check
Germany: Garderobe

CONTROL ROOM
Room at the rear of the auditorium (in a proscenium theatre) where lighting and sometimes sound is operated from. Known in the US as the BOOTH. The stage manager calling the cues is very often at the side of the stage (traditionally stage left) but in some venues they may be in the control room also. The control room is usually soundproofed from the auditorium so that communications between operators cannot be heard by the audience. A large viewing window is obviously essential, as is a show relay system so that the performance can be heard by the operators. Obviously if sound is being mixed, the operator should be able to hear the same as the audience, so some control rooms have sliding or removable windows, or a completely separate room for sound mixing. Where possible, the sound desk is moved into the auditorium so that the operator can hear the same as the audience.
Also known as the BOX.

COURTYARD THEATRE
Originally, a temporary or permanent performance space established in the courtyard part of an inn or public house in Elizabethan England. It consisted of a raised platform stage at one end of the courtyard, surrounded by lower level seating or standing, along with viewing positions on balconies and windows that already existed around the courtyard. Elizabethan purpose-built theatres used the same layout. The term now refers to a theatre built along the same lines - a thrust stage with seating on at least one level around the edges, and a lower seating location across the floor area surrounding the stage. 

CUPOLA
Architectural dome on the roof of a theatre or other building. 

CYCLORAMA
Usually shortened to just cyc (pronounced sike). The Cyclorama is a curved plain cloth or plastered wall filling the rear of the stage or TV studio. Often used as a sky backing to a traditional set, or as the main backing for a dance piece etc. The term is often loosely applied to a blue skycloth, or any flattage at the rear of the stage. Although strictly a cyc should be curved, most cycs are flat with curved wraparound ends. A more effective backing can be obtained by hanging a sharkstooth gauze just in front of the plain white cyc which gives a hazy effect of distance.
From Greek Cyclos (circle) and Horama (view or vision).
The first plaster cyclorama in the UK is believed to be at the Festival Theatre, Cambridge (1929)
See also BOUNCE, ISORA. The German equivalent term is operafolie.

DEUS EX MACHINA
Latin for God in the Machine. A mechanical device used in Greek classical and medieval drama to lower an actor playing God from the flies above the stage to resolve the conflict in a play.
The mechanical crane that carried the DEUS EX MACHINA was known as MECHANE.
The term sometimes refers to a character which has a similar function in a more modern drama.

DRENCHER
System of pipes arranged at the top of a safety curtain (aka Iron) to drench it with water in the event of fire. The water prevents it buckling as it descends.

DRESSING ROOMS
Rooms containing clothes rails and mirrors (often surrounded with lights) in which actors change into their costumes and apply make-up. Dressing Room doors have a list of the actors contained within.
See also GREEN ROOM.

END ON
End-On Stage Layout Plan (theatrecrafts.com) Traditional audience seating layout where the audience is looking at the stage from the same direction. This seating layout is that of a Proscenium Arch theatre.
Also known as Proscenium Staging.
The end-on stage can be split into 9 areas: upstage right, upstage centre, upstage left, centre stage right, centre stage, centre stage left, downstage right, downstage centre, downstage left.
See also THRUST, IN THE ROUND, TRAVERSE.

FLY FLOOR(S)
High working platform at the side(s) of the stage from which the flying lines are handled. Often are also the site for socket panels for connecting flown lighting apparatus to dimmers, and also sometimes a lighting position. Known in the US as Fly Gallery.

FLY TOWER
Extension of the stage walls up to allow scenery to be flown up until it is out of sight of the audience, and to support the GRID. Known as the "flies". The ideal fly tower should be more than twice the height of the pros. arch, and is said to have "full flying height". The load on the grid is transferred to the ground via the walls of the theatre. Known in the US as the Fly Loft, and in Europe as the Stage Tower.

FOH
See FRONT OF HOUSE.

FORESTAGE
That part of the stage which projects from the proscenium into the auditorium. See Apron.

FOYER
Part of the front of house area of the theatre into which the audience first arrive on entering the theatre. The foyer normally contains: Box Office, Toilets, Entrance to auditorium, Bar, Concession / merchandising stand.

FRONT OF HOUSE (FOH)
1) Every part of the theatre in front of the proscenium arch. Includes foyer areas open to the general public.
2) All lanterns which are on the audience side of the proscenium and are focussed towards the stage.
The backstage areas of the theatre are known as Rear of House (ROH).

FRONT TABS
House curtains.

GALLERY
1) One or more raised seating platforms towards the rear of the auditorium.
2) See LOADING GALLERY.

GANTRY
A bridge-like structure at high level inside a building designed to carry equipment (e.g. lighting equipment, cameras etc). Sometimes equipped with a walkway for access. 

GODS
Colloquial term for the Upper Circle of the auditorium.

GRAND CIRCLE
See CIRCLE.

GRAND CURTAIN
(US) The main house tabs in a venue. Normally a variation of blue or red in colour, although a more neutral grey is often better for scenes played in front of it, or for taking colours and gobos as tab warmers.

GRAND DRAPE
See GRAND CURTAIN.

GREEN
(obsolete term) The part of the stage visible to the audience.

GREEN ROOM
Room close to the stage (i.e. the green) for the actors to meet and relax before or after going on stage. See the link below for some possible derivations of the term.
More about Green Room

GRID
1) The support structure close to the top of the fly tower on which the pulleys of the flying system are supported. Constructed from metal or wooden beams. (Italian: gratticia / graticciata / graticcio)
2) Arrangement of scaffolding from which lanterns are hung in a performance space with no flying facilities. Grid is short for GRIDIRON.

GRIDIRON
See GRID.

HEAVENS
The roof or canopy over an Elizabethan stage (such as Shakespeare's Globe in London), often painted with a representation of the night sky with stars, moon, zodiac signs etc.

HIPPODROME
Originally, a Greek stadium for horse or chariot racing, the term was applied to multi-purpose venues built in the early 1900s which often had flexible stages surrounded by audiences on all sides. The stage floor was often moveable to reveal a water tank, which was sometimes able to rise up. 
London Hippodrome at Theatrecrafts.com

HOUSE
1) The audience (eg 'How big is the house tonight ?') The count of how many are in the audience is known as the House Count, and may be different from tickets sold, as some people may not attend. 
2) The auditorium (eg 'The house is now open, please do not cross the stage')

HOUSE CURTAIN
Same as HOUSE TABS. The house curtain is the main set of curtains ('tabs') in the venue. Not every show will use the tabs, but it's often nice to save the audiences' first view of the set for a special moment as the show starts, not as 'wallpaper' while they're coming into the auditorium. However, this entirely depends on the nature of the show. Known as GRAND CURTAIN in the US. See also TAB WARMERS.
Spanish: Bambalinón

HOUSE TABS
The main set of curtains ('tabs') in the venue. Not every show will use the tabs, but it's often nice to save the audiences' first view of the set for a special moment as the show starts, not as 'wallpaper' while they're coming into the auditorium. However, this entirely depends on the nature of the show. Known as GRAND CURTAIN or HOUSE CURTAIN in the US. See also TAB WARMERS.
Spanish: Bambalinón
Dutch: voordoek (front curtain)

IN THE ROUND
Theatre in the Round is a form of audience seating layout where the acting area is surrounded on all sides by seating. There are often a number of entrances through the seating. Special consideration needs to be given to onstage furniture and scenery as audience sightlines can easily be blocked.
Stage managers and directors often use the idea of a clock face to describe actor positions on stage (e.g. the aisle nearest the technical point is described as the 12 O'clock position, with other aisles described as 3, 6 and 9 O'clock.)
See also ARENA, THRUST, END ON, TRAVERSE.

IRON
See SAFETY CURTAIN.

ISOPTIC
The characteristic of entertainment venues that enables the audience to all have an equal view of the stage or screen by raking the auditorium and off-setting the seats so that no view is obstructed. 

LIFT
The orchestra pit and/or sections of the stage may be mounted on lifts to make moving of heavy items (e.g. piano etc.) easier. Sometimes the forestage doubles as the orchestra pit by use of a lift.

LOBBY
See Foyer.

LOGE
(esp.US) Seating area in traditional proscenium arch venues. Exact location varies according to the venue, but is usually a 'box' position at the dress circle level. (From the French Loge)

LOGGIA
Italian architectural term for a covered balcony or walkway, usually open to the exterior on one side. In the theatrical world, a Loggia is a partially enclosed seating area or box away from the usual seating areas. 

MARQUEE
Marquee outside Radio City Music Hall, July 2017 (USA) A permanent canopy over the entrance of the theatre, where the name of the show (and sometimes the stars) are displayed. 

MEZZANINE
Architecturally, a mezzanine is a raised floor supported by columns. In a theatre, it refers to the balcony seating area (or the lowest of the balconies in a larger theatre). 

MULTIFORM THEATRE
A reconfigurable performance space which can satisfy the requirements of a wide range of creative styles and venue types, consisting of lifts, adjustable floor heights, movable seating banks and variable acoustic qualities. 
A great example is the Wyly Theatre in Dallas, Texas

O.P.
End-On Stage Layout Plan (theatrecrafts.com) Opposite Prompt side of the stage. Stage Right. (ie Actors right when facing audience).

OPERA
1) European terminology meaning Opera House - lavishly decorated proscenium theatre with orchestra pit. See TOSCA.
2) Musical form. Highly dramatic and stylised form where the text is completely sung.
See also OPERETTA, OPERA HOUSE.

ORCHESTRA
1) In Greek Theatres, the central performance area used by the Chorus or for dancing.
2) Refers to the main seating area of the auditorium at floor level.
3) Colloquially known as 'the band' the musicians who perform from the orchestra PIT.

ORCHESTRA PIT
See PIT.

PAC
(USA) Performing Arts Center. The building (particularly in an educational organisation) where performances are staged and/or rehearsed. 

PAINT FRAME
Large vertical wooden frame from which cloths are hung for painting. The frame is often winchable for easy access.

PARODOS
Parodos (also parode and parodus, plural parodoi, Ancient Greek) is a term used in the theater of ancient Greece, referring either to a side-entrance, or to the first song sung by the chorus after its entrance from the side wings.

PARTERRE
(French: On the ground). Refers to the audience members in the pit / stalls / lowest part of the auditorium in front of the stage. Originally, the term was used in the 16th century to refer to a formal ornamental garden, but by the mid-17th century, it was increasingly used to refer both to the ground level of a theatre where spectators stood to watch performances and to the group of spectators who occupied that space.
Wikipedia entry

PASS DOOR
A fire-resisting door in the wall of the proscenium arch which is the only correct access between the auditorium and the stage.

PASSARELLE
A walkway leading beyond the proscenium arch around the audience side of the orchestra pit. Enables actors to get very close to the audience, and often used in musical theatre or cabaret performances. There are problems with sound reinforcement (feedback is much more likely due to being closer to the front of speakers) and video relays are often used as the conductor is no longer visible.
PASSERELLE means Footbridge or gangway in French.

PERCH
1) A lighting position (often on a platform) at each side of the stage, immediately behind the proscenium.
Some theatres use the term for vertical boom positions in front of the proscenium in the house.
The plural is PERCHES. They may be named by position (e.g. Front Perch, Rear Perch, SL Perch etc).
2) An ancient unit of measurement, used since the 9th century, and abolished in the UK in 1963. One perch is equal to 16.5 feet, or 5.03 metres. 

PIT
Short for ORCHESTRA PIT. The area housing the orchestra or band. Originally, a lower section between the front of the stage and the audience, although now describes any area around the stage housing the musicians. 
The term was used in the Globe Theatre in London for the lower area immediately in front of the stage where the 'groundlings' watched the performance. This area was also known as the YARD.

PLASTER LINE
See SETTING LINE.

PORTA REGIA
('Royal Door') The central entrance in the scaenae frons, the permanent architectural background to the stage of a Roman theatre. 

PROMPT CORNER
Area, traditionally on the stage left side of the stage, from which the stage manager (or DSM) controls ('prompts') the performance, from the prompt desk.

PROMPT SIDE (PS)
End-On Stage Layout Plan (theatrecrafts.com) Usually stage left side of the stage, containing the prompt corner.

PROP ROOM
Either a room in which the theatres' collection of props is stored, or an offstage room where props for the show are kept, ready for the actors to pick them up.

PROS.ARCH
Short for Proscenium Arch.

PROSCENIUM ARCH
The opening in the wall which stands between stage and auditorium in some theatres; the picture frame through which the audience sees the play. The "fourth wall". Often shortened to Proscenium or Pros Arch.
In some older theatres, the Proscenium Arch is ornate and painted to contrast with the surrounding walls, to really make it stand out. Nothing outside the Proscenium Arch was part of the show.
However, as there are many different audience layouts now, many theatres (particularly multi-purpose studio theatres) have no Proscenium Arch at all, or it may not be decorated as such.
See END ON.
Italian: Boccascena
French: cadre de scène

RAKE
See Raked Stage.

RAKED AUDITORIUM
Audience seating area which is sloped, with it's lowest part nearest the stage.

RAKED STAGE
A sloping stage which is raised at the back (upstage) end. Many theatres with a 'stalls' seating area used to be built with raked stages as a matter of course. Today, the stage is often left flat and the auditorium is lifted to stage level and above to improve the view of the stage from all seats. A rake is expressed as a ratio (eg a 1:25 rake rises by 1cm vertically over 25cm horizontally).
See also ANTI-RAKE.

REAR OF HOUSE (ROH)
1) The backstage areas of the theatre. See also FOH (Front of House). Also sometimes known as Back of House.
2) Abbreviation for Royal Opera House, London. 
Royal Opera House

SAFETY CURTAIN
Safety Curtain at the Theatre Royal Haymarket, London (From the Flickr page) A fireproof "curtain" that can be dropped downstage of the house tabs in a proscenium theatre to separate the audience from the stage in the event of fire.
A Safety Curtain is required by most UK licensing authorities for theatres of traditional design. The regulations also require that it is raised and lowered at least once in view of each audience (usually during the interval). Usually made from sheet metal and electrically operated, these curtains were originally of iron construction faced with asbestos and lowered by gravity using a hydraulic damping system. Colloquially known as the "iron".
Some Safety Curtains are painted - the iron at the Theatre Royal Drury Lane has a beautiful design with the text "For Thine Especial Safety".
The musical Billy Elliot uses a false iron as a scenic device with a pair of doors in it, which would not be permitted for a real iron.
The line on the stage where the fire curtain drops, usually a short distance from the downstage edge of the stage, is known as the FIRE CURTAIN LINE and cannot be obstructed by any fixed scenery.
The first Safety Curtain is believed to date from 1794 at the Theatre Royal Drury Lane, when a (literal) iron curtain complete with water tanks at roof level were installed at the insistence of Richard Brinsley Sheridan, the theatre manager at the time. His architect / builder was Henry Holland. Unfortunately, the curtain failed to operate when a fire occurred in 1809, as the water tanks had emptied, and the iron had rusted.
Also known as FIRE CURTAIN, IRON or ASBESTOS. See also DRENCHER.

SCENE DOCK
High-ceilinged storage area adjacent to the stage, sometimes used for building and storing flats and other scenery.

SETTING LINE
Imaginary line running across the width of the stage, in line with the proscenium arch, which is marked on the groundplan and is used as a reference when planning set and furniture layouts etc. Usually the furthest downstage anything can be set without fouling the house tabs.
Known in some theatres as the PLASTER LINE - this refers to the upstage edge of the proscenium wall.
See also CENTRE LINE.

SHAKESPEARE
The Globe Theatre was a theatre in London associated with William Shakespeare.
It was built in 1599 by Shakespeare's playing company, the Lord Chamberlain's Men, on land owned by Thomas Brend and inherited by his son, Nicholas Brend and grandson Sir Matthew Brend, and was destroyed by fire on 29 June 1613.
A second Globe Theatre was built on the same site by June 1614 and closed in 1642.
A modern reconstruction of the Globe, named 'Shakespeare's Globe', opened in 1997 approximately 750 feet (230 m) from the site of the original theatre.

SHOP
(US) Section of the theatre where scenery is constructed (Scene Shop), or props are made (Prop Shop).
Often shortened to 'Shop'.

SKENE
Greek word (skēnē pronounced skay-nay) referring to the area at the rear of the acting area in an ancient performance space. The skēnē was originally a building or tent, but was sometimes painted onto scenery.

SLOAT
Now obsolete term for a piece of Victorian stage machinery first mentioned in 1843.
A sloat is a set of vertical rails or runners which were used to carry a platform for raising or lowering profile scenery, groundrows etc through a cut (narrow trap) in the stage floor. Believed to be a variant of 'slot'.

SMOKE POCKET
A vertical steel channel on the upstage edges of the proscenium arch in which the edges of the fire curtain travel, designed to stop smoke travelling around the fire curtain.
JR Clancy website

SPRUNG FLOOR
Usually, a permanently installed wooden floor which has rubber pads underneath it to enable the floor surface to absorb the shock of a performer dancing or jumping on it. This kind of floor is common in rehearsal studios and sports venues (it's also known as a Sports Floor, and is termed 'semi-sprung' if it has rubber pads).
Sections of the floor are locked together to ensure the floor surface moves without opening up gaps or creating trip hazards. 
A fully sprung floor is common in many theatres, and is an entirely wooden structure where the floor is supported by long joist beams across the stage, so the floor naturally flexes. These floors are especially loved by dance companies, however, there sometimes needs to be additional structural support under the floor to enable it to carry a heavy set. 
Padded dance floor rolls are available to provide some shock absorption if it's not possible to work on a sprung floor. 
Dance work on non-sprung floors is not recommended for long periods. 

STAGE
The part of the theatre on which performances happen, adjacent to the auditorium. See also ARENA, END ON, THRUST, IN THE ROUND.

STAGE DOOR
The backstage entrance to the theatre, usually on a different side of the building from the public entrance. Performers and technicians enter here. Large theatres normally have a stage door keeper, who takes messages for performers and acts as a security guard for the entrance. There's normally a separate phone line to the stage door, and calls can sometimes be put through to dressing room phones. Some venues operate a signing-in system, and the stage door noticeboard is an important reference point for information about local accommodation, union membership and rules particular to that theatre. 
Some popular shows have large groups of audience gathering around the stage door after the show to meet the cast, and to take photos with them. It's important that the audience respect the performers' needs to leave work and get home in a timely manner, and while some shows (particularly those active on social media) have well-established 'photo opportunities' with cast, there should be no expectation that a particular performer will want to participate. Cast and crew members often just want to go home when they leave their workplace. 

STAGE HOUSE
The part of the theatre upstage of the proscenium arch, which contains the stage, wings, fly tower, fly floors, grid etc. 

STAGE TOWER
See FLY TOWER.

SUBSTAGE
The under-stage area in a theatre. Depending on the complexity of the stage machinery, this may be a highly engineered area, with machines operating stage lifts, or it may be an empty room in which stage equipment is stored. 
In London's West End theatres, the sub stage area is configured for each show if stage automation and lifts are used. For Billy Elliot, the Victoria Palace Theatre had to be excavated to allow for the house lift to be installed. 

SUNBURNER
Historic combination gas light array and ventilation system built into many theatres with gas lighting (pre-electricity). 

THEATRON
1) Refers to the auditorium / seating area of an ancient Greek or Roman theatre.
2) Two scene preset compact manual control desk made by Century Lighting. 
3) 3D model archive project for creating accurate (and amazing) VRML models of old theatre buildings. (Windows operating system only).
Theatron VR website

THRUST
Form of stage which projects into the auditorium so that the audience are seated on at least two sides of the extended piece. See also END ON, IN THE ROUND.

THUNDER RUN
Long series of channels down which wooden cannonballs are rolled to give a realistic thunder rumble effect. Built into the roof of some older theatres, but mostly now unused (for safety reasons).
The Bristol Old Vic has restored their Thunder Run in 2016 for their 250th anniversary.
History of Sound Effects for the Stage

TIERED SEATING
Seating area with rows increasing in height away from the stage area. Used to improve sightlines to the stage, to ensure that the whole audience gets an unobstructed view of the actors. 

TIRING HOUSE
In Shakespearean times, this was the room wear the actors waited, adjacent to the stage. The room is now known as the GREEN ROOM.

TOSCA
Trans-Opera Security and Care Association. European organisation (since 1997) created to safeguard the architectural heritage of opera houses and the form of opera.
TOSCA website

TRAP
An opening through the stage floor.
A grave trap is a lowered rectangular section used in Hamlet etc.
A cauldron trap is a simple opening through which items can be passed into a cauldron on stage.
A star trap is a set of triangular sprung flaps in the stage floor through which an actor can be propelled from a lift below stage.
A diaphragm trap can close around an object allowing it to penetrate a previously solid wall with no visible gap around it. . 
A pivot trap is a doorway or opening with a central pivot which enables it to rotate (like a revolving door). 
The Vampire Trap was invented for James Planché's 1820 adaption of Polidori's The Vampyr. It involved two spring leaves that parted under pressure and immediately reclosed. Placed in the floor or stage wall, it could give the impression a figure was passing through solid matter.
The Corsican Trap, made for Dion Boucicault's 1852 adaption of Alexandre Dumas' The Corsican Brothers, involved an ascending track, on which a wheeled cart could be run, rising up out of the stage through a 'bristle' trap - a trapdoor covered with bristles painted to match the scenery. Once on the stage and in view, the track was covered by a sliding arrangement reminiscent of that of a roll-top desk; towhit, nothing was seen except the ghost rising up through the floor and gliding across the stage. This trap is also sometimes called a Ghost Glide. (Vampire Trap and Corsican Trap definition from 'The Cabinet of Dr Casey')
More about Traps

TRAVERSE
Form of staging where the audience is on either side of the acting area.
Also known as ALLEY or AVENUE staging. 
See also IN THE ROUND, END ON, THRUST.

UNDERCROFT
A ground-level parking area underneath a building that occupies the footprint of that building (and sometimes extends to other service areas around the structure).

UPPER CIRCLE
(UK) Highest balcony in the auditorium. Also known as the GODS. Normally has a very steep view down to the stage, and highly raked seating.

USITT
United States Institute of Theatre Technology.
Founded in 1960. Publisher of Theatre Design and Technology and Sightlines journals, which are available online (see Publications in the Theatrecrafts.com Archive section).
USITT Website

WING SPACE
The distance between the edge of the performance space that the audience can see, and the wall of the theatre. A lot can be achieved with very narrow wing space, with careful planning and well choreographed stage management team, but you need at least 12 feet to make things possible, and a lot more than that if there are large set pieces to move. 

In the London production of Sunset Boulevard, a car had to appear from the stage right wing, and as the theatre didn't have enough space, the car had to be stored hanging vertically from the fly floor above. It was winched down into position, with its' rear wheels still in the air, and the actors stepped into it. As the front of the car moved on stage, the rear was able to be fully lowered into position, and the audience were unaware of the complexities.