The order 
T-polyomino consists of a vertical line of 
squares capped by a horizontal line of three squares centered
on the line.
T-Polyomino
See also
L-Polyomino, Skew Polyomino, Square Polyomino, Straight PolyominoExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "T-Polyomino." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/T-Polyomino.html