A set is a collection of objects. The objects that are in the set are known as elements or members of the set.

If x is an element of a set A, we writex\in A. We read this as ‘x is an element of set A’ or ‘x is in A’.

If x is not an element of a set A, we write x \notin A.

The set B is called a subset of a set A if every element of B is also an element of A. We write B ⊆ A. This expression can also be read as ‘B is contained in A’ or ‘A contains B’.

An example is given at the right using Venn Diagram. Here, A=\{0,1,2,3,4\},\ B=\{0,1,2\}.