What is object-oriented programming and what are its four pillars?

OOP organizes code around objects (data + methods). Four pillars: 1) Encapsulation: bundling data with methods that operate on it, hiding internals (private/public). 2) Abstraction: showing only essential features, hiding complexity. 3) Inheritance: creating new classes from existing ones (parent → child). 4) Polymorphism: same method name, different behavior (overriding in subclasses). Example: Animal class with speak() → Dog.speak() returns "Woof", Cat.speak() returns "Meow".