Octagon

An octagon or 8-gon is a polygon that has exactly 8 sides.

Regular octagon

All sides of a regular octagon are the same length. Each corner is 135°. All corners added together equal 1080°.

The amount of space a regular octagon takes up is

{\text{Area}}=2(1+{\sqrt {2}})a^{2}.

a is the length of one of its sides.

Another way to write it is

{\text{Area}}=2a^{2}({\sqrt {2}}+1).

This shape is called an octagram. It has one regular octagon in the middle.
The octagonal prism has 2 octagons in it: one on the top, and the other on the bottom.
A non-regular octagon
Making an octagon by folding paper

Polygons
Special cases, including regular polygons with their own names, in parentheses List of polygons by number of sides
1–10 sides	Henagon Digon Triangle Quadrilateral Pentagon Hexagon Heptagon Octagon Nonagon Decagon
11–20 sides	Hendecagon Dodecagon Tridecagon Tetradecagon Pentadecagon Hexadecagon Heptadecagon Octadecagon Enneadecagon Icosagon
21–100 sides (selected)	Icosikaitetragon (24) Triacontagon (30) Triacontadigon (32) Tetracontagon (40) Pentacontagon (50) Hexacontagon (60) Heptacontagon (70) Octacontagon (80) Enneacontagon (90) Hectogon (100)
>100 sides	257-gon Chiliagon (1,000) Myriagon (10,000) 65537-gon Apeirogon (∞)
Star polygons (5–12 sides)	Pentagram Hexagram Heptagram Octagram Enneagram Decagram Hendecagram Dodecagram
Triangles	Equilateral triangle Isosceles triangle Scalene triangle Right triangle Acute and obtuse triangles
Quadrilaterals	Square Rectangle Rhombus Parallelogram Trapezoid Kite Antiparallelogram