cone
Cone
a triangular pyramid
A rectangular prism is a three dimensional shape. The two bases are squares and the four sides are rectangles.
2
It is sometimes called the base.
Octagonal prism
prism
Cone
a triangular pyramid
Octagonal pyramid
A pyramid.
rectangular pyramid
cube square prism
The Area of its base times the height of the shape.
A 3-dimensional shape with eight sides is an octahedron. If you would refer to a 3-dimensional octagon, just call it that, people will understand what you mean. Or maybe you mean an octagonal prism. That's an octagon, except it is extended into the third dimension by stretching it, so it has an octagonal base but the other sides are triangles all connecting at one point above the octagon.
A rectangular prism is a three dimensional shape. The two bases are squares and the four sides are rectangles.
A bicone is a three-dimensional shape swept by revolving an isosceles triangle around its base of unequal length, or by joining two identical right circular cones, base to base.