actor: a person who performs in a play
backdrop: a large cloth (or paper) that is painted and hung as scenery
blackout: when all lights are simultaneously turned off to indicate the end of a scene
blocking: a plan that indicates where an actor stands and moves
“Break a leg!”: a theatre expression meaning "Good luck!"
cast: the actors in a play
center stage: the middle portion of the stage floor
character: a person in a story that an actor plays
choreographer: a person who plans and teaches movements - like dances and fight sequences - to actors
costume director: a person who designs and makes the costumes actors wear
cue: a signal that tells an actor when to speak or move
curtain call: actors gather on stage at the end of a performance to receive applause
director: the person who interprets the play and provides direction to the actors and designers
downstage: the area of the stage that is closest to the audience
dress rehearsal: the last rehearsal before a play opens with actors in full costume
Foley artist: a person who creates sounds for film or theatre using a variety of objects to enhance the sound effects 
giving focus: an actor on stage does not move or talk so that audience attention is drawn to another actor who is moving or talking
improvisation: a drama that is not scripted, but is made up as you go
lighting designer: a person who plans what lights are used and when they are used to help create a setting
makeup designer: a person who makes actors faces resemble the characters they are playing
mime: an actor who performs without words
monologue: a scene when only one actor speaks
offstage: the area of the stage that is not seen by an audience
onstage: the area of a stage where actors perform
pantomime: a story performed without words  
producer: the person who arranges the financing of a play
prop: short for properties. Any object used by an actor.
proscenium: a decorative frame that arches around the stage's acting area
script: a play in written form
set: the acting area including props and scenery 
set designer: the person who designs the scenery for a play
sound designer: the person who selects the music and sounds used in a play
stage crew: people who set up scenery and change it between scenes of a play
stage directions: instructions given to actors to tell them when and where to move on stage
stage left: the area of stage that is on the actor's left
stage manager: the person who makes sure a performance runs as planned
stage right: the area of stage that is on the actor's right
taking focus: the actor speaks confidently and makes intentional movements in a way that gets the audience's attention 
theater: movie show
theatre: on a stage, live, with actors
upstage: the back of the stage or the area that is the farthest away from the audience