undercut -- to speak with a softer tone and lower pitch than the previous line
underplay -- to use a softer tone, less energy, and a more casual manner than previously
understudy -- performer in the show who studies another role and is prepared to substitute in case of emergency
unities -- restrictions set by Aristotle that a play should take place in one day, at one place and with a single plot line
unit set -- uses flats, screens, curtains, platforms, and stairs that can be rearranged to change locales
universal theme -- a theme or message in a play understood by all men at all times
up-left center -- that part of the playing area farthest from the audience and just left of center as you face the audience (the actor’s left)
uplight -- light that comes from underneath a performer, either from footlights or through a grated or Plexiglas stage floor
upstage -- area on the stage area farthest away from the audience. The term dates back to the days when the stage was raked away from the audience so that actors had to literally walk upstage
upstaging -- to cross deliberately to a place upstage of another actor and assume a full front or one-quarter position, thereby forcing the other performer to turn to a three-quarter position in order to talk with the upstager