Abstraction is a fundamental concept in object-oriented programming (OOP) that allows developers to hide complex implementation details and focus on essential functionalities. In C#, Abstraction is achieved through abstract classes.

An abstract class is a class that cannot be instantiated which means that we cannot create an object of that class. An abstract class can contain attributes and methods like any other class however it may also contain abstract methods which are blueprint methods meant to be implemented by derived classes.

We can create an abstract class by adding the abstract keyword before the class definition. For-example, lets create an abstract class called Shape:

Similarly, we can create an abstract method by adding the keyword abstract before its return type. An abstract method does not have any body - it is simply a blueprint:

The purpose of this is to create a blueprint for other classes. This helps in simplifying the code. To understand this better, let's look at the Polymorphism task from Chapter 5:

In the above example, we never intend to use the Shape class however we still had to write some bogus implementations of the getArea and calculatePerimeter methods inside the Shape class. We can somewhat simplify this code by making the Shape class abstract, apart from that we can also make the getArea and calculatePerimeter methods abstract.