Real Dictionary

upstage
When an actor is upstage or moves upstage, he or she is or moves towards the back part of the stage.

upstage in American English
of or having to do with the rear of a stage
to draw the attention of the audience away from (a fellow actor) and to oneself by moving upstage so that the other actor must face away from the audience
toward or at the rear of a stage
adjective: of, pertaining to, or located at the back of the stage
adverb: on or toward the back of the stage
noun: the rear half of the stage
transitive verb: to overshadow (another performer) by moving upstage and forcing the performer to turn away from the audience

upstage in British English
to move upstage of (another actor), thus forcing him or her to turn away from the audience
adjective: of or relating to the back half of the stage
adverb: on, at, or to the rear of the stage
noun: the back half of the stage