abstract class

from The Free On-line Dictionary of Computing (8 July 2008)

abstract class

   <programming> In {object-oriented programming}, a {class}
   designed only as a parent from which sub-classes may be
   derived, but which is not itself suitable for instantiation.
   Often used to "abstract out" incomplete sets of features which
   may then be shared by a group of sibling sub-classes which add
   different variations of the missing pieces.

   (1994-11-08)