in the area behind the stage in a theatre, especially the rooms in which actors change their clothes or where equipment is kept

We went backstage after the show to meet the actors. 演出结束后我们去后台跟演员们见面。

backstage workers 幕后工作人员

If something happens backstage, it is not generally known about.

The organizers say it's a fair contest but who knows what goes on backstage? 组织者说这是一场公平的比赛，但谁知道背后有什么名堂呢？