Common Lisp the Language, 2nd Edition
When a generic function is called with particular arguments, it must determine the code to execute. This code is called the effective method for those arguments. The effective method is a combination of the applicable methods in the generic function. A combination of methods is a Lisp expression that contains calls to some or all of the methods. If a generic function is called and no methods apply, the generic function no-applicable-method is invoked.
When the effective method has been determined, it is invoked with the same
arguments that were passed to the generic function. Whatever values it
returns are returned as the values of the generic function.