**An eight-sided shape is known as an octagon.** Octagons are flat shapes with eight straight sides.

Octagons have certain characteristics that set them apart from other shapes. Octagons can be regular or irregular. When an octagon is regular, it has all equal sides. If the sides are not equal, the octagon is classified as irregular. The octagon can also be convex, with no angles pointing inwards or concave, with an angle pointing inwards. To be classified as an octagon, the shape in question must have a closed diameter with all sides connecting up. Generally, a regular octagon has 135-degree interior angles and 45-degree exterior angles.