The 15-puzzle is a sliding puzzle consisting of a frame divided into a 4x4 grid, containing 15 numbered tiles and one empty space. The objective is to arrange the tiles in numerical order, from 1 to 15, by sliding them into the empty space. Players can only move tiles adjacent to the empty space, making strategic moves necessary to achieve the goal. The puzzle is a classic example of a combinatorial puzzle and has been popular since its invention in the 19th century, challenging both casual players and puzzle enthusiasts alike.