The set of values or objects that can be used as the first components of the ordered pairs of a relation.

This is not to be confused with the domain of a relation, which is the set of the first components of the ordered pairs of a relation. Therefore, given a relation ℜ from E to F, dom(ℜ) ⊆ E, that is, the domain of the relation is a large subset of the set of departure.

### Examples

- In this illustration of a relation between the set E and the set F, the set E = {2, 3, 4, 5} is the set of departure of the relation. The domain of this relation is {2, 4}.

- Consider the relation
*y*= 2*x*+ 1, where*x*is a natural number.

The set of departure is the set of whole numbers: {0, 1, 2, 3, 4, …}

The set of destination is the set of odd whole numbers: {1, 3, 5, 7, 9, …}