Octagon
An octagon is a geometric two-dimensional shape that has a total of eight sides. All sides on an octagon are convex, i.e. there are no concavities. Stop signs are made in the form of an octagon. A regular octagon is that in which all the sides are of equal length and all angles are the same number of degrees.
In architecture, an octagon house is a house built in an octagonal shape. Monticello is the most famous example.