In computer networking, master/slave is a model for a communication protocol in which one device or process (known as the master) controls one or more other devices or processes (known as slaves). Once the master/slave relationship is established, the direction of control is always from the master to the slave(s). The County of Los Angeles, saying the term master/slave may be offensive to some of its residents, has asked equipment manufacturers not to use the term. Some manufacturers prefer the term primary/secondary.
Other communication protocol models include the client/server model, in which a server program responds to requests from a client program, and the peer-to-peer model, in which either of the two devices involved can initiate a communication session.