In geometry, a shape, or polygon, with eight sides is called an octagon. A common example of an octagon in the real world is the stop sign. The octagon is also used in architecture, and umbrellas often come in an octagonal shape.
"Octa-" is a prefix derived from the Greek and Latin languages meaning "eight." In addition to eight sides, an octagon also has eight internal angles and eight vertices. The interior angles of an octagon add up to 1080 degrees. A regular octagon has all sides of the same length, and all internal angles are 135 degrees. Another eight-sided figure, the eight-sided star, is called an octagram.