An interface is a class-like concept in Object Oriented Programming. An interface is a collection of method declarations. but an interface has no variable declarations or method bodies. it describes a set of methods that a class can be forced to implement means Once you create an interface you need to implement all the methods specified in that interface.
An interface can be used to define a set of “constant”
An interface can be used as a type concept.
Variable and parameter can be of interface types.
Interfaces can be used to implement multiple inheritance like hierarchies.
Interface and abstract classes
Difference between class and interface in C#?