Three or more lines that converge to form a two-dimensional shape is called a plane. Like lines, planes can be literal or implied, defining spaces or creating an area of interest. They are most often found in a square or rectangular shape (as in walls or corridors), but can be any other shape, regular or irregular, so long as it is flat and possesses no perceived depth.
|Image credit: Bernstein, Fred A. "The Good Earth." Metropolitan Home. March 2009. 75. (Overlay mine.)|