The Free On-line Dictionary of Computing (30 December 2018):

Lisp Object-Oriented Programming System

   (LOOPS) An object-oriented extension of Lisp from the
   Intelligent Systems Laboratory at Xerox Palo Alto
   Research Center.  It is used in the development of
   knowledge-based systems.

   See also CommonLoops.

   ["The LOOPS Manual", D.G. Bobrow & M. Stefik, Xerox Corp
   1983].