What do you call the domains of a relation?

Question

I have noticed that for binary relations $R_2 \subseteq A \times B$, that the set A is called the domain and B is called the codomain. What about other n-ary relations where n > 2? For example, is there a standard name for the sets X, Y and Z for a relation $R_3 \subseteq X \times Y \times Z$? Are they all just called domains?