Sudoku is a popular number placement puzzle. Many newspapers print a sudoku each day, often next to the crossword. The word sudoku is Japanese for “single numbers.”

A sudoku consists of a grid of 81 boxes, each of which is either blank or contains a single number. The trick is to write numbers in the blank boxes so that every digit from one to nine appears just once in each horizontal and vertical line. The origin is Japanese — sūdoku combines sū(ji), "number," and doku(shin), "single status." The game's original name was sūji wa dokushin ni kagiru, "the numbers are restricted to single status." Not quite as catchy.

Definitions of sudoku
  1. noun
    a number puzzle in which the numbers 1 through 9 must be placed into a grid of cells so that each row or column contains only one of each number
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    type of:
    mystifier, puzzle, puzzler, teaser
    a particularly baffling problem that is said to have a correct solution
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