 Similarly, a polyomino is said to be "horizontally" or "row convex" if its intersection with any horizontal line is convex.A polyomino is said to be "convex" if it is row and column convex.A polyomino is said to be "directed" if it contains a square, known as the "root", such that every other square can be reached by movements of up or right one square, without leaving the polyomino.