One of the all-time classic video game
s, invented in the mid 1980s
In its original form, you rotate tetrominoes (groups of 4 connected squares) as they fall into a 10-unit-wide bin;
these stick in place as soon as they try to move down but are blocked by another piece,
and the next tetromino appears at the top of the screen.
When you complete a row of 10 squares across the screen without any holes, those 10
squares flash and disappear, and the blocks above them drop down a row. If this leaves
hanging bits, they remain hanging. If two or more blocks are completed at the same time,
they both drop out, and you get a score bonus for doing so. If four rows drop at the same
time, which can only be done by standing the long, straight piece on end, this
is called a Tetris. The general strategy is to try to avoid covering holes, since
this makes the rows containing those holes impossible to drop until the row(s) covering
the holes are dropped, although an important strategy is to recognize when you can drop
an upper row with a move that seems to cover a hole but doesn't actually because the
covering square(s) are immediately dropped.
There are two main variations: Marathon mode, where you just keep playing until you
can't fit any more pieces into the bin (or, specifically, until the next piece doesn't
fit on the screen without overlapping some other piece), and Goal mode, where you
have a set goal, usually a certain number of lines to drop, and after reaching it, the
board resets to some initial configuration (often not empty) and you get a new
goal. Generally, the Goal mode is used in arcade games where the marathon mode is too
short of a game, but both modes are used in computer game versions.
Tetris spawned dozens of imitators and variations. There were games with bigger,
smaller, and disconnected pieces, different goals, differently-sized bins, and pieces
with various sorts of special effects when they landed; games where two people played
against each other, and each line dropped by one player caused some bad effect for the
other player (an idea revived by Super Puzzle Fighter 2 Turbo); games where two players played
cooperatively in a single, large grid; games based on hexagonal grids and
in 3D, etc.