What is concave and convex?

Answer 1

The best example would be to take a metal spoon that is shiny. Look at the spoon so the curved part is facing away from you. The dip you can see is called Concave. The other side that protrudes is called Convex. When you look at the concave side your face will appear squashed, wider at the top and bottom but very narrow in the middle. When you look at the convex side, your face will appear wide and fatter, almost like a football. This is because of the light rays reflective at a different angle.