offstage

US /ˌɑːfˈsteɪdʒ/
UK /ˌɑːfˈsteɪdʒ/
"offstage" picture
1.

away from the stage, out of the sight of the audience

:
The actor waited offstage for his cue.
You could hear the sound of thunder offstage.
1.

situated or taking place away from the stage, out of the sight of the audience

:
The offstage sounds created a sense of tension.
There was an offstage argument during the play.