In our daily life, we come across many patterns that characterize relations such as brother and sister, mother and child, teacher and student, etc. Similarly, in mathematics also, we come across different relations such as number a is less than number b, set A is subset of set B, and so on. In all these cases, we find that a relation involves pairs of objects in some specific order. In this unit, you will learn how to link pairs of objects from two sets and then introduce relations between the two objects in the pair. You also learn here about special relations which are called functions.