The crossword solution for the term SUDOKU FILL-IN is DIGIT, which is a five-letter word. Sudoku is a logic-based number-placement puzzle, in which the objective is to fill a 9x9 grid with digits so that each column, each row, and each of the nine 3x3 subgrids that compose the grid contain all of the digits from 1 to 9. The challenge of the game is to fill in the grid with the correct digits without repeating any numbers in the same row, column, or 3x3 subgrid.