Full Idea
A relation is 'reflexive' on a set if every member of the set bears the relation to itself.
Gist of Idea
A relation is 'reflexive' on a set if every member bears the relation to itself
Source
Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], Ch.0)
Book Reference
Enderton,Herbert B.: 'A Mathematical Introduction to Logic' [Academic Press 2001], p.5