Inheritance is a basic concept of Object-Oriented Programming where
the basic idea is to create new classes that add extra detail to
existing classes. This is done by allowing the new classes to reuse
the methods and variables of the existing classes and new methods and
classes are added to specialise the new class. Inheritance models the
“is-kind-of” relationship between entities (or objects), for example,
postgraduates and undergraduates are both kinds of student. This kind
of relationship can be visualised as a tree structure, where ‘student’
would be the more general root node and both ‘postgraduate’ and
‘undergraduate’ would be more specialised extensions of the ‘student’
node (or the child nodes). In this relationship ‘student’ would be
known as the superclass or parent class whereas, ‘postgraduate’ would
be known as the subclass or child class because the ‘postgraduate’
class extends the ‘student’ class.

Inheritance can occur on several layers, where if visualised would
display a larger tree structure. For example, we could further extend
the ‘postgraduate’ node by adding two extra extended classes to it
called, ‘MSc Student’ and ‘PhD Student’ as both these types of student
are kinds of postgraduate student. This would mean that both the ‘MSc
Student’ and ‘PhD Student’ classes would inherit methods and variables
from both the ‘postgraduate’ and ‘student classes’.