Wikipedia: Tetromino

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A tetromino, also spelled tetramino, is a geometric shape composed of four squares or cubes. Compare with domino which is composed of two squares.

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

Counting rotations in two dimensions as equivalent, there are seven possible shapes:

I (also called "stick", "straight")
```
 _ _ _ _
|_|_|_|_|
```
Square (also called "O", "package", "block")
```
 _ _
|_|_|
|_|_|
```
T
```
 _ _ _
|_|_|_|
  |_|
```
L
```
 _
|_|
|_|_
|_|_|
```
J (also called "inverted L", "Gamma". This piece is a reflection of L but cannot be rotated into L in two dimensions; this is an example of chirality. However, in three dimensions, this piece is identical to L.)
```
   _
  |_|
 _|_|
|_|_|
```
S
```
   _ _
 _|_|_|
|_|_|
```
Z (Reflection to S. See "J", above.)
```
 _ _
|_|_|_
  |_|_|
```

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

left screw (chiral in 3D)
```
 _ _
|_|_|
  |+| unit cube on top of +
```
right screw (chiral in 3D)
```
 _ _
|_|_|
|+|   unit cube on top of +
```
branch (nonchiral in 3D)
```
 _ _
|_|+| unit cube on top of +
  |_|
```

Some people refer to the pieces by the colour in which they are drawn in a particular implementation of the Tetris game, but those colours vary from implementation to implementation so this is not very sensible. For example, in [Vadim Gerasimov]? the original PC Tetris "Tetris & Dr. Mario" for Super NES, the red piece is I.

Colors of pieces in various implementations (under construction)
Piece	[Microsoft Tetris]?	[The New Tetris]?
I
I
I
I
I
I
I

Note that the box art of The New Tetris reverses the colors of the L and J pieces and the S and Z pieces.