It could be a triangular based pyramid whose technical name is a tetrahedron.
Faces.
a cube
Faces on solid figures are like when you look at a square you see a flat wall type surface.
sphere
cone
octagonal prism (i guessed)
Solid figures are normally named after their number of faces.
Pyramid
A pyramid.
A square or rectanglular pyramid are the only solid figures that have exactly five faces.
A polyhedron is a solid whose faces are polyhedra, so the question is rather meaningless.
Those figures are called triangular prisms.