In general this refers to a space – usually an enclosed room, or booth – where the operations of something are handled, the central control point. In radio and television production, this refers to the room that houses the equipment used to bring all the audio and video signals together into a composite signal that’s broadcast or recorded. All the different cameras and microphones are fed into video switchers and audio mixers here. Similarly in theater applications, this is generally where all the audio signals are mixed, additional recorded sound effects may be added, and where the lighting is controlled (though these may be in separate control rooms). In theater it is sometimes referred to as a “Bio-Box,” which comes from the Greek word “Bios,” or Way of Life. In a recording studio, the control room has a similar function. It’s where the engineers and producers sit and take care of making sure good signals get recorded as well as controlling, in many cases, what the band hears during a performance. Ideally, control rooms are designed to be carefully regulated in terms of sound isolation and accurate sound reproduction, as this is where the final decisions are made about how a recording will sound.
On some audio equipment – typically mixers – there are control room outputs and associated control room level (volume) and mix controls. This pertains to sending signals to the control room speakers, which are usually a specially selected set of very accurate speakers designed to enable producers and engineers to hear a true reference of the audio signals being recorded and mixed. In some cases these speakers are custom designed to properly react with the control room space. In other cases a control room space may be built with a specific set of speakers (and other equipment) in mind.