Inheritance is a common way of extending and reusing the functionality of a class. Delegation is a more general way to extend a classes behavior. Delegation extends a class by using other classes functions, subroutines and properties rather than inheriting them. Inheritance is inappropriate for many situations in which delegation works well.
For example, inheritance is useful for capturing a “is-a-kind-of” relationships because of their very static nature. However, “is-a-role-played-by” relationships are akward to model with inheritance. With delegation you get instances of classes that can play multiple roles.