Unicode is a industry standard which allows text / characters / symbols from nearly all writing systems of the world to be represented or manipulated by computers / electronic media.
*en.wikipedia.org/wiki/Unicode
UCS is the Universal Character Set, which is a character encoding of the Unicode that contains a very large database of abstract characters, each identified by a name and a corresponding integer.
*en.wikipedia.org/wiki/Universal_Character_Set
UTF is the Unicode Transformation Format, which is another character encoding of the Unicode to support a large range of characters. The basic difference between the UCS and the UTF is that initial encoding / characters of the UTF are same as the ASCII standard.
*en.wikipedia.org/wiki/UTF-8
Hope this helps...
Cheers
Aditya