The basic game pieces for Tetris. They are blocks consisting of four uniformly shaped squares in various configurations. There are seven types of tetrad; only five if you consider the fact that 2 are mirror images of each other.
Colloquially, the tetrads are often referred to by which Roman character they most roughly resemble. Thus we have “I”, “T”, “S”, “Z”, “L”, and “Inverse “L” shapes. The square is just… the square.
[][] [][]
Square
[] [] [] []
Line, or 'I'
[] [][] []
'T'
[] [] [][]
'L'
[] [] [][]
'Inverse L'
[] [][] []
'S'
[] [][] []
'Z'
Needed info: Need images for the tetrads
are these not tetr[o/i]minoes? http://en.wikipedia.org/wiki/Tetromino