An interface in software development defines a contract or agreement between different software components. It specifies which methods, functions, or properties are available without detailing the exact implementation of these methods. It acts as a sort of contract or agreement stating, "If you implement this interface, you must provide these specific methods or properties."

Interfaces are used to create a clear separation between the functionality of a component and its implementation. They allow different parts of software to interact with each other without knowing the exact implementation details.

In many programming languages such as Java, C#, TypeScript, etc., classes or structures can implement an interface by providing the methods and properties defined in that interface. This enables consistent use and interchangeability of different implementations of the same interface.

Interfaces play a vital role in building well-structured, modular, and maintainable software as they facilitate component interchangeability and can reduce dependencies on concrete implementations.