What is interface

Answer 1

100% abstract class

Answer 2

Abstract, the term signifies incomplete. The class which is incomplete is known as abstract class. So what can be incomplete in a class, its methods. So usually not defining a method in a normal class is illegal, but abstract class have the feasibility to not define a method. These have some benefits in implementing some algorithms.
That's it.
Thank you

Answer 3

so, what is the abstract class?