What is an Interface?

An interface is a declaration for a set of class members. It is a reference type that contains only abstract members such as Events, Methods, Properties, etc.

In the context of .NET interview questions, the correct answer to “What is an Interface?” would be:

An interface in .NET is a reference type that defines a contract for its implementing classes or structs. It contains only the declaration of methods, properties, events, or indexers but doesn’t provide any implementation for them. Implementing classes or structs must provide the implementation for all the members declared in the interface. Interfaces facilitate polymorphism, allowing objects of different classes to be treated uniformly if they implement the same interface. They are essential for achieving abstraction and enforcing a common behavior across multiple classes or structs in .NET applications.