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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.

For example, both of these statements would return precisely the same string, but accomplish it through different types of methods:

// ToString() is an instance method of the DateTime class.
//  Its result depends on the value of each DateTime instance.
return DateTime.Now.ToString();
 
// String.Format is a static method of the String class.
//  Its result is not related to any instance of the String.
return String.Format("{0}", DateTime.Now);

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.