名詞 greenroom:

1. a backstage room in a theater where performers rest or have visitors

green.room

n.（名詞）
A waiting room or lounge in a theater or concert hall for the use of performers when they are off-stage.
演員休息室：劇場或音樂廳里后臺供演員休息的房間或休息廳

來源：
[So called because such rooms were originally painted green]
[因原先劇場演員休息室被刷成綠色，故得名]