Sudoku are logic puzzles in which an array of boxes, each an array of numbers or other unique symbols, has been designed, so that each row and column in the overall array contains the complete list of allowed symbols, and each box also contains that same complete list.
The original and most common Sudoku consists of a 9 x 9 grid of cells, divided into nine 3 x 3 boxes, and the unique symbols are the numbers from one to nine. However, this is not a mathematical puzzle, and letters or other symbols could be used.
In the puzzle as presented, symbols are missing, and the object of the game is to find the unique pattern of symbols that satisfies the conditions, using logic. A presented puzzle with more than one possible solution would usually be considered defective.