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

Universal Character Set
ISO 10646
ISO/IEC 10646-1
UCS

    (UCS, ISO/IEC 10646) A 1993 ISO and
   IEC standard character set, also known as "Universal
   Multiple-Octet Coded Character Set".

   UCS comes in a 16-bit variant called UCS-2 and a 32-bit
   variant called UCS-4, which is composed of 16-bit UCS-2
   "planes".  So far only one 16-bit plane has been defined,
   which is known as the Basic Multilingual Plane.

   The implementation of UCS is still in its infancy, though some
   moves, such as the Java language defining a character to be
   16 bits, are suggestive.

   [Relationship with Unicode?]

   (1997-07-04)