SUDOKU
Put simply, Sudoku (or 'Su Doku', or 'Su-doku') is a number-placement puzzle based on a square grid, typically 9 squares by 9, giving 81 squares in all. The puzzle is further divided (by bold gridlines) into 9 boxes or 'regions', each a square measuring 3 squares by 3.
Figures from 1 to 9 (known as 'givens') are already inserted in some of the squares; to complete the puzzle, a player must insert the missing numbers so that each row, each column, and each region contains the numbers 1 to 9 once and once only, without any repeats.
The level of difficulty depends upon the number of givens in any puzzle, and the ease with which a player can compute the missing numbers by the use of logic.