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