In show business, the green room is the space in a theatre or similar venue that functions as a waiting room and lounge for performers before and after a performance, and during the show when they are not engaged on stage. Green rooms typically have seating for the performers, such as upholstered chairs and sofas.
Possible sources of the term
The specific origin of the term is lost to history, which has led to many theories and claims. One story is that London's Blackfriars Theatre (1599) included a room behind the scenes, which happened to be painted green; where the actors waited to go on stage. It was called "the green room". Some English theatres contained several green rooms, each ranked according to the status and the salary of the actor: one could be fined for using a green room above one's station.
Richard Southern, in his studies of Medieval theatre in the round, states that in this period the acting area was called The Green. This central space, often grass-covered, was used by the actors, while the surrounding space and circular banks were occupied by the spectators. From this source then The Green has been a traditional actors' term for the stage. Even in proscenium arch theatres there was a tradition that a green stage cloth should be used for a tragedy. The green room could thus be considered the transition room on the way to the green/stage. Technical staff at some West End theatres (such as the London Coliseum) still refer to the stage as the green.
Another theory is that the room was originally painted green to "relieve the eyes from the glare of the stage." On the other hand, early stage lighting was by candlelight, so the "glare" might be apocryphal, a modern reference to electric stage lighting. It is sometimes said that the term green room was a response to limelight, though the name is merely a coincidence – "limelight" refers to calcium oxide, not to the fruit or colour. Furthermore, limelight was invented in 1820 and the term "green room" was used many years prior to that.
It is possible that "green room" might be a corruption of scene room, the room where scenery was stored which doubled as the actors' waiting and warm-up room.
Many actors experience nervous anxiety before a performance and one of the symptoms of nervousness is nausea. As a person who feels nauseous is often said to look "green", suggesting that the "Green Room" is the place where the nervous actors wait.
According to one theory, long before modern makeup was invented the actors had to apply makeup before a show and allow it to set up or cure before performing. Until the makeup was cured, it was green and people were advised to sit quietly in the green room until such time as the makeup was stable enough for performing. Uncured makeup is gone, but the green room lives on.
In Shakespearean theatre actors would prepare for their performances in a room filled with plants and shrubs. It was believed that the moisture in the topiary was beneficial to the actors' voices. Thus the green room may refer to the green plants in this stage preparation area.
The term green room can alternatively be traced back to the East End of London, England. In Cockney rhyming slang, greengage is stage, therefore greengage room is stage room and like most rhyming slang it gets shortened, hence green' room. This information came from comedian and dancer Max Wall. It should be noted, however, that Rhyming Slang can be traced only as early as the 1840s, whereas the phrase "green room" predates this by several centuries, making such an etymology unlikely.
Green is also thought to be a calming and soothing colour.
In Shakespeare's day, the actors waited in a "tiring house" probably because actors were attired (put on or changed costumes) in this space. Here it is mentioned by Peter Quince as he plans for his acting troupe to rehearse in the woods:
QUINCE: Pat, pat; and here's a marvellous convenient place for our rehearsal. This green plot shall be our stage, this hawthorn-brake our tiring-house; and we will do it in action as we will do it before the duke.— Midsummer Night's Dream (approx 1595) - Act 3 Scene 1
...she took us up into the Tireing-rooms and to the women's Shift, where Nell was dressing herself and...then below into the Scene-room, and...here I read the Qu's (cues) to Knepp while she answered me, through all her part of Flora's Figarys...
- Thomas Shadwell's Restoration comedy, A True Widow (1678), mentions in Act Four: Stanmore : "No madam: Selfish, this Evening, in a green Room, behind the Scenes, was before-hand with me..."
- The term "green room" is mentioned in Colley Cibber's Love Makes a Man (1701). "I do know London pretty well, and the Side-box, Sir, and behind the Scenes; ay, and the Green-Room, and all the Girls and Women~Actresses there.'
- In his Life of Samuel Johnson (1791), James Boswell mentions visits by his subject to the Green Room at the Drury Lane Theatre.
- In 1792, Joseph Haslewood published a collection of memoirs of the actors and actresses of the London theatres entitled, The Secret History of the Green-Room, while 1796 saw the first edition of John Roach's similarly themed, Authentic Memoirs of the Green-Room.
- In the Jane Austen novel Mansfield Park (1814), when the Bertram children convert the billiard room into a theatre, Tom Bertram notes, "And my father's room will be an excellent green-room. It seems to join the billiard room on purpose."
- In the 1853 Charlotte Brontë novel Villette the narrator refers to the green-room when preparing for a performance in an amateur play.
- Jerome K. Jerome's first book comically describes his stint in English theatre during the late 1870s. "There was no green room. There never had been a green room. I never saw a green room, except in a play, though I was always on the lookout for it."
- The green room is mentioned in the Sherlock Holmes short story The Man with the Twisted Lip by Sir Arthur Conan Doyle. "When an actor I had, of course, learned all the secrets of making up, and had been famous in the green-room for my skill."
- The Green Room, an upscale cocktail bar in Northampton, MA, serves as the central hub for concert-goers and performers before and after shows at the surrounding music venues. It's primarily green decorum harkens back to the historic style of such rooms in theaters.
- The American Heritage Dictionary of the English Language, William Morris editor, 1971
- Brewer's Dictionary of Phrase & Fable, Millennium Edition, revised by Adrian Room, 1999
- The Concise Oxford Companion to the Theatre, edited by Phyllis Hartnoll, Oxford University Press, 1972, pg 220
- Old theatre days and ways By William John Lawrence via Google Books quoting in turn An Actor's Notebook by George Vandenhoff
- Brewer's Dictionary of Phrase & Fable, Millennium Edition, Revised by Adrian Room
- "The Straight Dope: Why is the waiting room for talk-show guests called the "green room"?".
- "De Proverbio - Electronic Journal of International Proverb Studies. Proverbs, Quotations, Sayings, Wellerisms".
- Glossary of Technical Theatre Terms at theatrecrafts.com
- Voices from the World of Samuel Pepys By Jonathan Bastable pg 111, David and Charles Limited (2007) via Google Books
- "World Wide Words: Green room".
- The life of Samuel Johnson, LL.D. By James Boswell, Mowbray Morris, pg 122, via Google Books Boswell
- Brontë, Charlotte, Villette, Dover, 2007, pp. 112 and 119.
- On the Stage--and Off: the brief career of a would-be-actor, Jerome K. Jerome, pp 74-75, via Internet Archive 
- The New Annotated Sherlock Holmes: Volume I, Sir Arthur Conan Doyle, pg 191