Definition of Abstraction. a concept or idea not associated with any specific instance; "he loved her only in the abstract--not in person". the act of withdrawing or removing something. the process of formulating general concepts by abstracting common properties of instances.

Abstract Classes Compared to Interfaces. Abstract classes are similar to interfaces. You cannot instantiate them, and they may contain a mix of methods declared with or without an implementation. However, with abstract classes, you can declare fields that are not static and final, and define public, protected, and private concrete methods.