Klotski (from Polish klocki—wooden blocks) is a sliding block puzzle thought to have originated in the early 20th century. The name may refer to a specific layout of ten blocks, or in a more global sense to refer to a whole group of similar sliding-block puzzles where the aim is to move a specific block to some predefined location.

Like other sliding-block puzzles, several different-sized block pieces are placed inside a box, which is generally in 4×5 size. Among the blocks, there is a special one (usually the largest) which must be moved to a special area designated by the game board. The player is not allowed to remove blocks, and may only slide blocks horizontally and vertically. Common goals are to solve the puzzle with a minimum number of moves or in a minimum amount of time.

From: Wikipedia, https://en.wikipedia.org/wiki/Klotski