What is an interface?

An interface is a contract that specifies a set of methods that a class must implement, without providing the method bodies. It defines what operations are available but not how they are performed. In languages like Java and C#, interfaces allow multiple inheritance of type, enabling a class to implement several interfaces. For example, in Java you can declare interface Flyable { void fly(); } and a class Bird implements Flyable { public void fly() { ... } }. Interfaces promote loose coupling, abstraction, and polymorphism, making code more modular and easier to maintain.