Add the text of use of inheritance (#22097)

guide/english/java/inheritance/index.md

@@ -8,6 +8,16 @@ Java inheritance refers to the ability of a Java Class to `inherit` the properti
 *   The Class that extends or inherits is called a **subclass**
 *   The Class that is being extended or inherited is called a **superclass**
 
+## Why use inheritance in java
+- For Method Overriding (so runtime polymorphism can be achieved).
+- For Code Reusability.
+
+## Terms used in Inheritance
+- Class: A class is a group of objects which have common properties. It is a template or blueprint from which objects are created.
+- Sub Class/Child Class: Subclass is a class which inherits the other class. It is also called a derived class, extended class, or child class.
+- Super Class/Parent Class: Superclass is the class from where a subclass inherits the features. It is also called a base class or a parent class.
+- Reusability: As the name specifies, reusability is a mechanism which facilitates you to reuse the fields and methods of the existing class when you create a new class. You can use the same fields and methods already defined in the previous class.
+
 Thus, inheritance gives Java the cool capability of _re-using_ code, or sharing code between classes!
 
 Let's describe it with the classic example of a `Vehicle` class and a `Car` class :