This document provides an overview of object-oriented programming (OOP) concepts in C#, including classes, objects, inheritance, encapsulation, and polymorphism. It defines key terms like class and object, and explains how C# supports OOP principles such as defining classes with methods and properties, extending classes through inheritance, hiding implementation through encapsulation, and allowing polymorphic behavior through function overloading and overriding. Abstract classes and sealed modifiers are also covered. The document is intended to help explain basic OOP concepts in C# to readers.