Answer:   Its declared as abstract. It can have abstract and non-abstract methods. It cannot be instantiated. Its implementation must be provided by derived classes.

Answer:   An abstract class is an incomplete class or special class which can't be instantiated. The purpose of an abstract class is to provide a blueprint for derived classes and set some rules what the derived classes must implement when they inherit an abstract class.

We can use an abstract class as a base class and all derived classes must implement abstract definitions. An abstract method must be implemented in all non-abstract classes using the override keyword. After overriding the abstract method is in the non-Abstract class. We can derive this class in another class and again we can override the same abstract method with it.