Define reflexive relations

A relation $R$ in a set $A$ is called reflexive if $(a,a) \in R$, for every $a \in A$.

A reflexive relation is the one in which every element maps to itself. For example, consider a set $A$ = {1, 2}. Now, the reflexive relation will be $R$ = {(1, 1), (2, 2), (1, 2), (2, 1)}. Hence, a relation is reflexive if:

$(a, a) \in R$ $\forall$ $a \in A$