Universal multiple-octect Coded character Set ( see ... )
Other name of the new character set standard known as ISO/IEC 10646.
UCS is the first offcially standardized coded character set with the purpose to eventually include all characters used in all the written languages in the world (and, in addition, all mathematical and other symbols).
To be able to give every character of this grand repertoire a unique coded representation, the designers of UCS chose a uniform encoding, using bit sequences consisting of 16 or 31 bits (in the two coding forms, UCS-2 and UCS-4). This is the reason for the phrase "multi-octet" in the name of the standard.
As a related argument :
Unicode is a coded character set specified by a consortium of major American computer manufacturers, primarily to overcome the chaos of different coded character sets in use when creating multilingual programs and internationalizing software. From version 1.1 on, Unicode is scrupulously kept compatible with ISO/IEC 10646 and its extensions. The consortium is also an important contributor to the ISO work to further develop ISO/IEC 10646.
In short, Unicode can be characterized as the (restricted) 2-octet form of UCS on (the most general) implementation level 3, with addition of a more precise specification of the bi-directional behavior of characters, when used in the Arabic and Hebrew scripts. Unicode is presently at version 1.1. Extensions in the soon forthcoming version 2.0 will make it possible to access also the wider coding space of UCS-4, within this 16-bit encoding.