dressing room; green room; backstage area
The physical room or area where performers prepare and wait before going on stage. Also used broadly for the backstage area of a theater or performance venue.
The actor was reviewing the script in the dressing room.
Staff are coming and going through the backstage entrance.
behind the scenes; inside affairs; the inside story
Figurative use referring to the private, non-public aspects of a situation, especially in show business, politics, or organizations. Often implies insider knowledge or hidden dealings.
See also: 楽屋裏 (がくやうら)
Behind-the-scenes circumstances greatly influenced that decision.
The reporter was desperate to get the inside story.
The leading actress went into the dressing room and began getting ready.
The director revealed some behind-the-scenes details of the filming in an interview.
After the concert, I got to meet the singer backstage.
I visited my friend's dressing room and gave them flowers.
控室 is a general waiting room used by anyone (guests, staff, performers), whereas 楽屋 is specifically the performers' dressing room in a theater.
楽屋 specifically means the performers' dressing room, whereas 舞台裏 covers the whole backstage area or figuratively any hidden workings of an event.
Compound of 楽 (がく, 'music, performance') and 屋 (や, 'room, shop'). Originally referred to a room for musicians in traditional Japanese theater, later extended to dressing rooms and backstage areas in general.