Master/slave is a model of communication where one device or process has unidirectional control over one or more other devices. In some systems a master is selected from a group of eligible devices, with the other devices acting in the role of slaves.
In other words, "The master/slave configuration is basically used for load sharing purposes when two identical motors connected to two different drives are coupled to a common load". One drive is defined as the master and is configured for running in the speed-control mode whereas the other defined as slave is configured for running in torque-control mode.
In 2003, the County of Los Angeles in California asked that manufacturers, suppliers and contractors stop using "master" and "slave" terminology on products; the county made this request "based on the cultural diversity and sensitivity of Los Angeles County". Following outcries about the request, the County of Los Angeles issued a statement saying that the decision was "nothing more than a request". Due to the controversy,Global Language Monitor selected the term "master/slave" as the most politically incorrect word of 2004 .
The computer term "master/slave," which was banned as racially offensive by a Los Angeles County purchasing department, was named the most politically incorrect term of the year.[...] Among other terms on the top 10 list of politically charged words and phrases, issued by the word usage group Global Language Monitor, were "non-same sex marriage" to describe heterosexual unions, "waitron" for waiter or waitress and "higher being" for God, a term some people found too religious.