binary relation

noun2

1. •
   A subset of the Cartesian product A×A (the set of ordered pairs (a, b) of elements of A, alternatively written as A²).

   • Definition If E is a non-empty set then by an order on E we mean a binary relation on E that is reflexive, anti-symmetric, and transitive. — 2005
2. •
   A subset of the Cartesian product A×B.