In category theory, the domain of a morphism is its source object; that is, the domain of is . In particular, this is the case for a function: its domain is the set of elements to which it can be applied.
Other similar meanings of the term include:
A separate meaning of ‘domain’ occurs in domain theory, which is at the interface of logic and theoretical computer science. There a domain is a particular type of poset. Still another meaning occurs in algebra in the term integral domain.