Tetris is a puzzle video game created by Alexey Pajitnov, a Soviet software engineer, in the mid-1980s. In Tetris, falling pieces consisting of four connected blocks, known as tetrominoes, must be sorted into a pile. Once a horizontal line of the playfield is filled with blocks, the line disappears, granting points and preventing the pile from reaching the top. This gameplay has been used in approximately 220 versions across at least 70 platforms. Newer versions frequently add game mechanics, some of which have become standard. As of December 2024, Tetris is the second-best-selling video game series, with over 520 million sales, mostly on mobile devices.