Wikipedia: Tetromino

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A tetromino is a geometric shape composed of four squares/cubes. Compare with domino which is composed of two squares.

A popular use of tetrominoes is in the video game Tetris.

Counting rotations in 2d as equivalent, there are seven possible shapes:

I
```
 _ _ _ _
|_|_|_|_|
```
Square
```
 _ _
|_|_|
|_|_|
```
T
```
 _ _ _
|_|_|_|
  |_|
```
L
```
 _
|_|
|_|_
|_|_|
```
J (aka Inversed L? Usually considered identical to L, but note that it cannot be rotated into the same configuration. This is an example of chirality.)
```
   _
  |_|
 _|_|
|_|_|
```
S
```
   _ _
 _|_|_|
|_|_|
```
Z (usually considered identical to S, but note that it cannot be rotated into the same configuration. See "J", above.)
```
 _ _
|_|_|_
  |_|_|
```

When added the third dimension, there are three more patterns:

left screw
```
 _ _
|_|_|
  |X| unit cube on top of X
```

right screw

 _ _
|_|_|
  |X| unit cube underneath X

branch
```
 _ _
|_|X| unit cube on top of X
  |_|
```

Some people refer to the pieces by the colour in which they are drawn in the game Tetris, but those colours vary so this not very sensible. Nonetheless, the red piece is I.