The basic concepts in set theory include set, element, subset, union, intersection, and complement. The concept of a set was developed by German mathematician George Cantor (1845-1918). Sets are also used to define the concepts of relations and functions.

Finite set: The number of elements is finite Infinite set: The number of elements are infinite Empty set: It has no elements Singleton set: It has one only element Equal set: Two sets are equal if they have same elements Equivalent set: Two sets are equivalent if they have same number of elements

The most straightforward way to define a set is to say that it is an unordered collection of objects. These objects are called the elements of the set, and they can be organized into smaller collections called subsets.

Set theory begins with a fundamental binary relation between an object o and a set A. If o is a member (or element) of A, the notation o ∈ A is used. A set is described by listing elements separated by commas, or by a characterizing property of its elements, within braces { }. [ 5]