A rather vague term, used to indicate that systems which might operate separately are actually being used in some form of cooperative mode. The term is applied to hardware units, as in cross coupled, where a pair of inverting gates are used to form a latch circuit: the output of each gate serves as an input to the other. It is also applied to complete processors, as in loosely coupled and tightly coupled processors: there are substantial discrepancies in usage between different users of these terms, especially with respect to the precise overtone associated with the qualifying adverb. See also coupling, concurrency.