SubSet

Definition: Given a SeT S, a SeT T is a SubSet of S if, for all x belonging to T, x belongs to S.

T is a SubSet of S <-> T is contained in S

Example: Given the SeT of Complex Numbers: C = {a+bi: a, b belong to R, the real numbers}, then R = {x: x is a real number} is a SubSet of C.

This is true because any x in R can be represented as x+0i.