Abstraction and abstract class both are different things. Abstraction its thought process not real implementation . its mean showing only necessary things that sit no actual implementation how is about. Abstract class its one opp concept its used for different purpose. we can put all common functionality there .we can not create object for that type of class.

abstract class a type of class that object can not be create it contain abstract or not abstract method while abstraction is mechanism of data hiding.........

refer may article http://www.c-sharpcorner.com/UploadFile/0c1bb2/using-abstract-class-in-C-Sharp/

simply , abstract class implements abstraction for hiding complexity . Abstract class is a class with abstract methods & non abstract methods . Where abstraction is just a common english word which can be quoted as professional resume which describes in short by HIDING the complexity about any individual .