### A set ‘A’ is said to be a subset of B if every element of A is also an element of B, denoted as A ⊆ B. Even the null set is considered to be the subset of another set. In general, a subset is a part of another set.
Example: A = {1,2,3}
Then {1,2} ⊆ A.
Similarly, other subsets of set A are: {1},{2},{3},{1,2},{2,3},{1,3},{1,2,3},{}.
Note: The set is also a subset of itself.
If A is not a subset of B, then it is denoted as A⊄B.