In object-oriented programming (OOP), a class is a fundamental concept that acts as a template for creating objects. It defines properties (attributes) and behaviors (methods) that the objects created from the class can have. For instance, a class named 'Car' might have properties like color and make, and methods like accelerate and brake. Objects, known as instances of the class, are created based on this blueprint. Classes provide a means for abstraction and encapsulation, allowing complex systems to be modeled in a manageable and reusable way.