The implementation of the object system manipulates classes, methods, and generic functions. The object system contains a set of generic functions defined by methods on classes; the behavior of those generic functions defines the behavior of the object system. The instances of the classes on which those methods are defined are called meta-objects.
The object system supplies a set of meta-objects, called standard meta-objects. These include the class standard-object and instances of the classes standard-method, standard-generic-function, and method-combination.
The class standard-method is the default class of methods defined by the defmethod and defgeneric forms.
The class standard-generic-function is the default class of generic functions defined by the forms defmethod, defgeneric, and defclass.
The class named standard-object is an instance of the class standard-class and is a superclass of every class that is an instance of standard-class except itself and structure-class.
Every method combination object is an instance of a subclass of class method-combination.