3D shapes, they have 3 dimensions ... Right, what about triangles? Triangles become pyramids. You're now a square based pyramid with 4 triangular faces and a square face for your bottom.

A pyramid with a square base is a square-based pyramid. Image caption, 3D shapes that are non-polyhedral include cylinders, cones, and spheres. At least one face is not a polygon. At least one ...