Octahedra have eight faces. The answer to this question actually lies in the shape's name because the prefix "octa-" means "eight."
An octahedron is a three-dimensional polyhedron with eight faces. All the faces on an octahedron will be congruent. The octahedron is one of a group of five polyhedron shapes known as Platonic solids, and it is the only one in the group with eight sides. A regular octahedron also has six vertices and 12 edges. A transparent model of an octahedron with all its correct vertices and edges will have three interior diagonals.