Use left / right to move the blocks, Up for rotating the blocks

Tetris  is a puzzle game originally designed and programmed by Alexey Pajitnov in June 1985, while working for the Dorodnicyn Computing Centre of the Academy of Science of the USSR in Moscow. He derived its name from the Greek numerical prefix "tetra-", as all of the pieces contain four segments, and tennis, Pajitnov's favorite sport.

The game (or one of its many variants) is available for nearly every video game console and computer operating system, as well as on devices such as graphing calculators, mobile phones, portable media players, PDAs and even as an Easter egg on non-media products like oscilloscopes. It has even been played on the sides of various buildings, with the record holder for the world's largest fully functional game of Tetris being an effort by Dutch students in 1995 that lit up all 15 floors of the Electrical Engineering department at Delft University of Technology.

While versions of Tetris were sold for a range of 1980s home computer platforms, it was the hugely successful handheld version for the Game Boy launched in 1989 that established the reputation of the game as one of the most popular ever. Electronic Gaming Monthly's 100th issue had Tetris in first place as "Greatest Game of All Time". In 2007, Tetris came in second place in IGN's "100 Greatest Video Games of All Time".

Gameplay

A pseudorandom sequence of tetrominoes (sometimes called "tetrads" in older versions) - shapes composed of four square blocks each - fall down the playing field. The object of the game is to manipulate these tetrominoes, by moving each one sideways and rotating it by 90 degree units, with the aim of creating a horizontal line of blocks without gaps. When such a line is created, it disappears, and any block above the deleted line will fall. As the game progresses, the tetrominoes fall faster, and the game ends when the stack of tetrominoes reaches the top of the playing field and no new tetrominoes are able to enter.

Tetris game manuals refer to the seven one-sided tetrominoes in Tetris as I, J, L, O, S, T, and Z - due to their resembling letters of the alphabet - but players sometimes use other names for the pieces, such as "stick" for I or "snake" for S. All are capable of single and double clears. I, J, and L are able to clear triples. Only the I tetromino has the capacity to clear four lines simultaneously, and this is referred to as a "tetris." (This may vary depending on the rotation and compensation rules of each specific Tetris implementation. For instance, in the Super Rotation System (see below) used in many recent implementations, certain rare situations allow T, S and Z to 'snap' into tight spots, clearing triples.)