Prop - A hand-carried object small enough to be lost 30 seconds before it is needed on stage.
Blocking - The art of moving actors on the stage in such a manor as not to collide with the walls, the furniture, the orchestra pit, or each other. Similar to playing chess, except that the pawns want to argue with you.
Blocking Rehearsal - A rehearsal taking place early in the production schedule where actors frantically write down movements which will be nowhere in evidence by opening night.
Lighting Director - Individual who, from the only vantage point offering a full view of the stage, gives the stage manager a heart attack by announcing a play-by-play of everything that's going wrong.
The Forebrain - The part of an actors brain which contains lines, blocking and characterization; activated by hot lights.
The Hindbrain - The part of an actors brain that keeps up a running subtext in the background while the forebrain is trying to act; the hindbrain supplies a constant stream of unwanted information, such as who is sitting in the second row tonight, a notation to seriously maim the crew member who thought it would be funny to put real Tabasco sauce in the fake Bloody Mary’s, or the fact that you need to do laundry Sunday.
Dress Rehearsal - Rehearsal that becomes a whole new ball game as actors attempt to maneuver among the 49 objects and ideas that the director added at 7:30 that evening.
Set - An obstacle course, which, throughout the rehearsal period, defies the laws of physics by growing smaller week by week while continuing to occupy the same amount of space.
Stage Crew - Group of individuals who spend their evenings coping with 50 minute stretches of total boredom interspersed with 30 second bursts of mindless panic.
Message Play - Any play which its director describes as "worthwhile", "A challenge to actors and audience alike", or "designed to make the audience think". Critics will be impressed both by the daring material and the roomy accommodations, since they're likely to have the house all to themselves.
Bedroom Farce - Any play which requires various states of undress on stage and whose set sports a lot of doors. The lukewarm reviews, all of which feature the phrase "Typical community theatre fare" in the opening paragraph, are followed paradoxically by a frantic attempt to schedule more performances to accommodate the overflow of crowds.
Set Piece - Any large piece of furniture which actors will resolutely use as a safety shield between themselves and the audience, in an apparent attempt to both anchor themselves to the floor, thereby avoiding floating off into space, and to keep the audience from seeing that they actually have legs.
Dark Night - The night before opening night when no rehearsal is scheduled so the actors and crew can go home and get some well-deserved rest, and instead spend the night staring sleeplessly at the ceiling because they're sure they needed one more rehearsal.
Green Room - Room shared by nervous actors waiting to go onstage and the precocious children whose actor parents couldn't get a baby-sitter that night, a situation which can result in justifiable homicide.
Actors (As defined by set designer) - People who stand between the audience and the set designer's art, blocking the view. That's also the origin of the word "blocking" by the way.