A Latin square played as a puzzle: each figure appears once in each row, column and box. Japanese, 数独 — short for 数字は独身に限る, "the digits must be single." The constraint is the whole pleasure.
Japanese 数独 (sudoku), a shortening of 数字は独身に限る (sūji wa dokushin ni kagiru, the digits must be single); the puzzle's whole rule is folded into its own abbreviated name.
A Latin square played as a puzzle, where each figure appears exactly once in every row, column and box. The constraint named in the word is the entire pleasure of solving it.