A static method is simply one that is disassociated from any instance of its containing class. The more common alternative is an instance method, which is a method whose result is dependent on the state of a particular instance of the class it belongs to.
The key difference to understand is that a static method can be called without setting up a proper instance of the class it belongs to.In a sense, it is a stateless method
For more info :
Why do ASP.NET AJAX page methods have to be static?
I hope this will help to you.