'self' is a reference to the instance of a class in Python. It allows access to instance variables and methods, ensuring that each object maintains its own state and behavior within class definitions.

In Python's object-oriented programming paradigm, the use of 'self' is fundamental for defining instance methods and accessing instance variables within a class. When you define a method in a class, the first parameter must be 'self', which is a convention, although you can technically name it anything. However, using 'self' helps maintain code readability and consistency across Python programs. When an instance of the class is created, 'self' refers to that specific instance, allowing you to access attributes and methods associated with it. This is crucial for maintaining the state of an object, as each instance can have its own unique attributes. For example, if you have a class Car with attributes like make and model, each instance of Car will hold its values for these attributes, and 'self' will provide access to them within the class methods. Without 'self', it would be impossible to differentiate between instance attributes and local variables, leading to confusion and errors in your code. Understanding how to use 'self' effectively is key to mastering object-oriented programming in Python, enabling you to create classes and objects that encapsulate both data and behavior cohesively.