A face is one of the polygonal surfaces of a polyhedron.
This rectangular prism has six faces. We can see three of them (blue, purple, and green); the other three are hidden from view. This polyhedron has eight faces. We can see five of them -- four rectangles (of which the blue, purple, and red ones appear to be square), and a green L-shaped six-sided figure (hexagon). The other three faces -- the bottom rectangle, the tall right-side rectangle, and the back L-shape -- can't be seen.
