It is any association between or among objects/elementsBinary Relation is any association or relationship existing between elements of one set, set of inputs called domain, and elements of another set, set of outputs called range. In short, it is a set of ordered pairs.

Reflexive/IrreflexiveSymmetricAntisymmetricTransitive

It is a relation that has exactly one output for every possible input. It must satisfy two rules: 1) if there is an input, there should be an output and 2) for each input, there is only one output

Domain the set of all possible inputsCodomain the set of all potential outputsRange the set of the actual outputs

1 -1 Function (Injective Function/Injection)Onto Function (Surjective Function/Surjection)1-1 Correspondence (Bijective Function/Bijection)