Offstage musicians and singers in popular music

Offstage musicians and singers are performers who play instruments and/or sing backstage, out of sight of the audience, during a live popular music concert at which the main band is visible playing and singing onstage. The sound from the offstage musicians or singers is captured by a microphone or from the output of their instrument, and this signal is mixed in with the singing and playing of the onstage performers using an audio console and a sound reinforcement system.

Source: Wikipedia — Offstage musicians and singers in popular music (CC BY-SA 4.0)