Question

definition of a subset

Answer 1

In mathematics, if we say set a is subset of set b ,it means all elements of set a are contained in set b
Definition..
Subset is a set whose all elements are contained in another set .

Answer 2

Let A,B are sets,

→We say that A is a subset of B when and only the all elements of set A are present in set B.

→A ⊆ B

For example,

A={1,2,3}
B={1,2,3,4,5,6,7}

Here the elements 1,2,3 which are present in set A are also present in set B.

So,A ⊆ B

Hope it helps