TITLE: What is the name for the shape formed by removing a square from the corner of a larger square?
QUESTION [7 upvotes]: Squares of consecutive numbers differ by the sum of those numbers, so $6^2 = 5^2 + 5 + 6$.  Geometrically, this is because the difference between the two squares is a pair of strips, $5$ and $6$ units long, that together form L-shaped polygon.
Is there a name for this L-shaped polygon?  I vaguely recall that the ancient Greeks had a name for this shape, but I can't find it anywhere.

REPLY [10 votes]: It's a gnomon. Euclid used it often. Here's an example from Book II, Proposition 6: