What is Octagon?
An octagon is a polygon made up of 8 sides. It has eight angles.
Octagon = Octa + gon where octa means eight and gon means sides.
There are 20 diagonals in an octagon as shown below.
The following figures are not octagons:
It is a heptagon as it has seven sides.  
It is a pentagon as it has five sides.  
It is a hexagon as it has six sides.  
It is a quadrilateral as it has four sides. 
Angles of an octagon:
An octagon consists of 8 angles. The sum of the angles of an octagon is 1080°.
In the given octagon, ∠A + ∠B + ∠C + ∠D + ∠E + ∠F + ∠G + ∠H = 1080°.
An octagon has 8 exterior angles. The sum of the exterior angles of an octagon is 360°.
Regular octagon: An octagon in which all sides and angles are equal. Each angle of a regular octagon is 135°.  Irregular octagon: An octagon in which all sides and all angles are not equal. Measures of angles of an irregular octagon are different but they all sum to 1080°. 
Real life examples
Some of the most popular examples of the octagon are the STOP signboard and umbrella.
Fun Facts about octagon
