green room

Attested at least as early as 1701.

green room (plural green rooms)

1. In a television studio, theatre or concert hall, the room where performers await their entrance.
   • 2016, Margaret Atwood, Hag-Seed, Chapter 12, page 80:

     There are three smaller rooms he can use as rehearsal space or dressing rooms or green rooms, according to need.

2. (surfing) The inside of a tube (cylindrical wave).
   • 1996, Surfer Bob‎:

     Never quite got covered up, but stood in the doorway to the green room with the lip feathering over my shoulders several times

• (room for performers): tiring-room, tiring-house