A method is an object that represents a modular part of the behavior of a generic function.
A method contains code to implement the method's behavior, a sequence of parameter specializers that specify when the given method is applicable, and a sequence of qualifiers that is used by the method combination facility to distinguish among methods. Each required parameter of each method has an associated parameter specializer, and the method will be invoked only on arguments that satisfy its parameter specializers.
The method combination facility controls the selection of methods, the order in which they are run, and the values that are returned by the generic function. The object system offers a default method combination type and provides a facility for declaring new types of method combination.
Section 7.6 (Generic Functions and Methods)