Domain

https://en.wikipedia.org/wiki/Domain

The domain is the source set in operations or relations on two sets.

Given two sets A and B, where ∀a ∈ A and ∀b ∈ B, set A is the domain:

• in set operations (union, intersection, etc.), e.g. A U B = {a ∨ b}

• in the dot product, A x B = {(a,b)}

• in relations on sets, aRb i.e. {(a,b)} = R ⊆ A x B

• in functions, f :: A -> B and f = {(a,b)}

The domain set is sometimes denoted by $A_{dom}$.