Solid OOPS

It's SOLID principle.

Check following which is from wikipedia

Initial	Stands for (acronym)	Concept
S	SRP [4]	Single responsibility principle a class should have only a single responsibility (i.e. only one potential change in the software's specification should be able to affect the specification of the class)
O	OCP [5]	Open/closed principle "software entities … should be open for extension, but closed for modification."
L	LSP [6]	Liskov substitution principle "objects in a program should be replaceable with instances of their subtypes without altering the correctness of that program." See also design by contract.
I	ISP [7]	Interface segregation principle "many client-specific interfaces are better than one general-purpose interface."[8]
D	DIP [9]	Dependency inversion principle one should "Depend upon Abstractions. Do not depend upon concretions."[8] Dependency injection is one method of following this principle.

Hi Pramod,

Please go through this link : 
http://www.c-sharpcorner.com/Blogs/47330/solid-principles.aspx

I am sure it will help you.

Cheers,
Prashant