Tetris basically defines "addictive" for an entire generation. Initially developed by a Russian and based on an ancient Roman game, Tetris was introduced to a wide audience through a software version developed for IBM. From there, it spread to the Nintendo gaming console, Gameboys, other home computers. Soon, pretty much everyone knew how to play Tetris, and had--at one time or another--become a bleary-eyed Tetris zealot.
The game is simple enough. Tetrominoes are shapes made up of little squares. The pieces all have different shapes and colors. The pieces fall down a kind of well, and you can rotate the shapes as they fall. The object is to get an entire horizontal row of squares (without any holes). When a row is completed, it disappears. But the tetrominoes fall fast and hard, and if you don't clear your squares before they're stacked to the top, you're out of luck.
The game is so addictive, in fact, that players may start seeing possible Tetris configurations in their daily life -- unevenly stacked books, a brick side of a building, or even dreams. It's so well-known, in fact, that it's given a name -- the "Tetris Effect."