The Free On-line Dictionary of Computing (18 March 2015):
Universal Character Set
(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?]