X 0208 is the standard Japanese
character set used on most computers. It consists of 6,879 characters—6,355 kanji
and a selection of punctuation, Latin, Cyrillic, and Greek characters.
The set was originally defined in 1983 as a replacement for JIS C 6226; it has been revised twice since then, in 1990 and 1997. Because of this, it's common to see the year written after the JIS code to clarify exactly which version of the set is being used (e.g. JIS X 0208-1990).
Each character in the JIS X 0208 set has a hexadecimal "kuten" number assigned to it. There are four digits in a character's kuten: the first two form a number between 21 and 74, while the last two form a number between 21 and 7E. The kuten value can then be shifted to determine the EUC or Shift-JIS encoding of the character.
At first, the set was controversial among Japanese typographers: although it contains many more kanji than anyone would ever need on a daily basis, it doesn't include many archaic or unusual kanji that are used in personal names or historical writings. The JIS X 0212 extension was created to attempt to solve this problem.