Our common sense understanding of the word slave pretty much clues us in to how it is used in audio/video production. The specific literal definition we are concerned with is; a machine or component controlled by another machine or component. When two devices are synchronized to one another it is necessary to have one be the master and the other the slave. The slave unit responds to commands or information from the master and is thus controlled by it. This is the basic principle behind all synchronization in audio and video. For example, if a computer system is following an analog tape machine (or video deck) it can be said to be “slaved” to it.