1855 in theatrical jargon, "to the rear of the stage," from up (adv.) + stage (n.). From 1901 as an adjective, 1916 as a noun. The notion in the verb (1921) is of drawing attention to oneself (and away from a fellow actor) by moving upstage, so that the other actor must face away from the audience. Related: Upstaged; upstaging.
Entries linking to upstage
Old English up, uppe, from Proto-Germanic *upp- "up" (source also of Old Frisian, Old Saxon up "up, upward," Old Norse upp; Danish, Dutch op; Old High German uf, German auf "up"; Gothic iup "up, upward," uf "on, upon, under;" Old High German oba, German ob "over, above, on, upon"), from PIE root *upo "under," also "up from under," hence also "over."
As a preposition, "to a higher place" from c. 1500; also "along, through" (1510s), "toward" (1590s). Often used elliptically for go up, come up, rise up, etc. Up the river "in jail" first recorded 1891, originally in reference to Sing Sing, which is up the Hudson from New York City. To drive someone up the wall (1951) is from the notion of the behavior of lunatics or caged animals. Insulting retort up yours (scil. ass) is attested by late 19c.
Sense of "period of development or time in life" first recorded early 14c., probably from Middle English sense of "degree or step on the 'ladder' of virtue, 'wheel' of fortune, etc.," in parable illustrations and morality plays. Meaning "a step in sequence, a stage of a journey" is late 14c. Meaning "level of water in a river, etc." is from 1814, American English.
Stage-name is from 1727. Stage-mother (n.) in the overbearing mother-of-an-actress sense is from 1915. Stage-door is from 1761, hence Stage-Door Johnny "young man who frequents stage doors seeking the company of actresses, chorus girls, etc." (1907). Stage whisper, such as used by an actor on stage to be heard by the audience, first attested 1865. Stage-manage (v.) is from 1871.
When the dog entered the stage, he upstaged the actress
she crossed to the upstage chair forcing the lead to turn his back to the audience
the dancers were directed to move upstage