Cohesion

Cohesion is a [design principle] and a measure of the degree to which the elements inside a module belong together. A module with high cohesion is one that groups together elements that are closely related in the [business domain].

Because modules with high cohesion tend to have fewer dependencies on other modules, highly cohesive systems tend also to be highly modular, with low coupling between components.

Achieving high cohesion requires good domain modeling. When the domain boundaries are not well understood or well designed, cohesion tends to be low and coupling tends to be high.