In topology it is common to use mapping to mean "continuous function", in order to avoid overuse of the word "continuous".
The domain? of a mapping is the set of elements from which the mapping is valid, that is the set of valid starting points of a mapping.
Sometimes one refers to a [partial mapping]? being a mapping from a set where only a subset of the elements are part of the domain. A [total mapping]? from a set S is a mapping where S itself is the domain.