offstage
US /ˌɑːfˈsteɪdʒ/
UK /ˌɑːfˈsteɪdʒ/

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.