Another suggestion for the "Ruby Singleton Classes" or "Exclusive Classes":

Sterile Classes

Class:   keeps structure and behaviour
Sterile: cannot create ( instances / objects )

The Term is currently unassigned:

http://www.google.com/search?q=sterile+classes

-

Concept of a "Sterile Class":

A Sterile Class is a Class, with all the abilities of the languages
Classes, exept:

  * It cannot be instantiated.
  * It is not part of the observable object-model

In Ruby, Sterile Classes are used to change the behaviour of _one_ object.

The Sterile Class
  * becomes _not_ part of the observable inheritance-chain.
    * e.g.: cannot be reached via
      obj.class,
      obj.superclass,
      obj.instance_of [...]
  * _becomes_ part of the non-observable inheritance-chain.
    * e.g.: method-resolution looks _first_ at the "Sterile Class"
      * internal implementation

[Thus, "Pseudo Class" would be possibly a right term, too - but already
used within CSS domain]

-

please look at the 1.3 version of the Diagramm:

http://lazaridis.com/case/lang/ruby/

"john" has an "Exclusive Sterile Class"
"john" is an instance of "Talker"
"john" has _no_ observable relation to its "Exclusive Sterile Class"

[observable via OOAD]

=> "[Exclusive] Sterile Class"
=> "Sterile Class"

-

"Talker" has an "Sterile Class" (Class:Talker)
"Class:Talker" keeps the structure and behaviour of class Talker.
thus "Class:Talker" is the "MetaClass" of class Talker.
=> MetaClass

but Talker is an instance of class "Class".
the MetaClass "Class:Talker" has no instances.

=> "Sterile Meta Class"

-

The terminology depends finally on the further development direction of
Ruby.

If it is planned to make the object model more OO like, and to implement
_real_ metaclasses, then it would be enouth to say:

"Attention: In the current implementation, a Ruby MetaClass is based on
"Sterile Classes".  Although they describe structure and behaviour of a
Class, they do not instantiate those classes. They are _not_ part of the 
inheritance-tree and thus _not_ part of the object-model. That's why the 
documentation referes them as "Sterile Meta Classes" "

..

-- 
http://lazaridis.com