Definitions for onstageˈɒnˈsteɪdʒ, ˈɔn-
Random House Webster's College Dictionary
on or onto the stage
Ref: (opposed to offstage ).
(adj.)of, pertaining to, or used in that part of the stage seen by the audience.
Origin of onstage:
situated or taking place on the area of a stage visible to the audience
on the stage
"it was time for her to go onstage"
towards, or onto the visible part of a stage
taking place in the part of a stage that is visible to the audience