A class which has atleast one abstract method is known as an Abstract class.
! Abstract Method - A method which has only method declaration but no method definition is known as an Abstract method.
! An abstract class cannot be instantiated by the keyword new.
! An abstract class should have atleast one child class, using child class instance variables only we can access abstract class features.
! The base class can be overridden by using 'override' keyword in derived class.
! An abstract method cannot also use the modifiers static or virtual.
! An abstract class cannot be sealed.
! Partially Abstract classes.
! Abstract class features we have to inherit to the child classes.