Explain the principles of object-oriented programming (OOP) and how they apply to PHP development.

Object-oriented programming (OOP) is a paradigm that promotes the use of objects and classes for organizing code. In PHP, classes encapsulate data and behavior, providing modularity and reusability. OOP principles include encapsulation, inheritance, and polymorphism. Encapsulation ensures data security by restricting access to certain properties and methods. Inheritance allows a class to inherit properties and methods from another class, promoting code reuse. Polymorphism enables objects of different classes to be treated as objects of a common superclass, enhancing flexibility in the codebase.