Which of the following is NOT one of the four main principles of OOP?

In the context of object-oriented programming (OOP), the four main principles are encapsulation, inheritance, polymorphism, and abstraction. These principles serve to organize code in ways that promote reusability, scalability, and the management of complexity.

Encapsulation refers to the bundling of data and methods that operate on that data within a single unit, typically a class. This allows for a clear interface for interacting with the object and protects the internal state of the object from unauthorized access.

Inheritance is a mechanism that allows a new class to inherit properties and behaviors (methods) from an existing class. This promotes code reuse and establishes a natural hierarchy between classes.

Polymorphism enables a single interface to represent different underlying forms (data types). This allows for methods to be used interchangeably, enhancing flexibility in code.

Procedural programming, on the other hand, is a programming paradigm based on the concept of procedure calls, where programs are structured as a sequence of procedures or routines. While it is a valid programming approach, it is not a principle of object-oriented programming. Thus, identifying procedural programming as not being one of the core principles of OOP is the correct choice.