Sudoku is the most popular logic puzzle in Japan also known as Suduko, Sudoko, Su do ku, Sodoku, Suduku. It is very simple to learn, requires no calculations, and provides a surprisingly wide variety of logic situations. From children to old can enjoy it for a pass-time. The game refers to a number placement puzzle also known as Number Place in USA. First Japanese title of this puzzle is "Suuji wa dokushin ni kagiru". It's means that number is limited only single (unmarried). But this title is too long, then it was abbreviated as "Sudoku". So "SU" means number, "DOKU" means single. The puzzle seems to have first been published in the USA before being noticed and then popularised in Japan.