Seven randomly rendered tetrominoes or tetrads - shapes composed of four blocks each - fall down the playing field. The object of the game is to manipulate these tetrominoes with the aim of creating a horizontal line of blocks without gaps. When such a line is created, it disappears, and the blocks above (if any) 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.

The seven rendered tetrominoes in Tetris are referred to as I, T, O, L, J, S, and Z. All are capable of single and double clears. I, L, and J are able to clear triples. Only the I tetromino has the capacity to clear four lines simultaneously, and this clear 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 "Tetris Worlds" rules used in many recent implementations, certain rare situations allow T, S and Z to 'snap' into tight spots, clearing triples.)

It is believed to be one of the best selling games of all time, mostly due to it's availability on a great amount of platforms. Tetris has been featured in Arcades, mobile gaming devices such as Nintendo's Game Boy, mobile phones, PDAs, personal computers and of course the web.

The music for the original Game Boy edition of Tetris titled "Music A" has become very widely known. It is a in fact a Russian folk tune called "Korobeyniki". To this day it is estimated that two our of three adults living in the US identify the tune as "The Tetris tune".

Tetris is a registered trademark of the Tetris Company LLC, but the game itself is not copyrighted in the US (games cannot be copyrighted, only patented, and any Patent claims to Tetris would be expired by today) ? which is why many Tetris clones legally exist.

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