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The two 3-Polyominoes are called triominoes, and are also known as the Trominoes. The left triomino above is ``Straight,'' while the right triomino is called ``right'' or L-.
See also L-Polyomino, Polyomino, Straight Polyomino
References
Gardner, M.  ``Polyominoes.''  Ch. 13 in The Scientific American Book of Mathematical Puzzles & Diversions.
  New York: Simon and Schuster, pp. 124-140, 1959.
 
Hunter, J. A. H. and Madachy, J. S.  Mathematical Diversions.  New York: Dover, pp. 80-81, 1975.
 
Lei, A.  ``Tromino.''  http://www.cs.ust.hk/~philipl/omino/tromino.html314