An octagonal prism has two octagon faces on either side, connected with eight rectangular faces for a total of 10 faces. An octagonal prism is the three-dimensional projection of a two-dimensional octagon, an eight-sided polygon.
A polygon describes any two dimensional figure that forms a closed loop. Any polygon can be turned into a prism by projecting it into a third dimension, giving it depth. An octagonal prism is derived from an octagon, which is why it contains an octagon on both ends. There are 10 faces, 16 vertices and 24 edges in any octagonal prism. The octagons on the end do not need to be regular octagons.