Sudoku is a popular number puzzle game that involves filling a 9x9 grid with digits so that each column, each row, and each of the nine 3x3 subgrids that compose the grid (also called "boxes", "blocks", or "regions") contain all of the digits from 1 to 9. The puzzle setter provides a partially completed grid, which typically has a unique solution. Players are required to use logic and deduction to solve the puzzle. The game became widely popular in the early 2000s and is enjoyed by people of all ages as a stimulating mental exercise.