there are 5 people on a stage without their face showing behind a red curtain
The people are waiting for their performance to start.
These people could be off stage waiting for their performance to start.
The 5 people on the stage may not be waiting for a performance to start at all.
People can be engaged in many activities for many reasons so people may not necessarily be waiting. Also there may be times when people can be behind a curtain on a stage when a performance is not about to start.