Coupling

Coupling is a much stronger and useful criterion than cohesion. It describes the interface, or flow of data values, between a called function (a server function) and a calling function (a client function).

Coupling can be implicit, with functions communicating through global variables, or explicit, when the client and server functions communicate through parameters. Implicit coupling is higher—it results in a higher degree of dependency between the client and server functions. Explicit coupling is lower: When functions communicate through parameters, it is easier to understand, reuse, and modify them.