Question

what does subset mean?

Answer 1

Let A be a set and B be a set, B is said to be a subset of A, if every element of B is also in A. The vice versa may or may not be true

Answer 2

In mathematics, especially in set theory, a set A is a subset of a set B if A is "contained" inside B. A and B may coincide. The relationship of one set being a subset of another is called inclusion or sometimes containment. Correspondingly, set B is a superset of A since all elements of A are also elements of B.