Anamorphosis is when an image is distorted but then made to appear normal again. Artists use anamorphosis to play tricks to surprise their viewers. They might want to hide an image that needs to be secret or make an image look just right from one particular viewpoint.
Anamorphosis often uses reflection. A very simple example is mirror writing. If you write something back-to-front it is hard for other people to read it until they hold it up to a mirror. More complicated techniques use curved mirrors that distort shapes as well as reverse them.
Another idea in anamorphosis is projection. Your own shadow is an example. It gets shorter or longer depending how high the sun is and what your shadow is cast onto. When the sun is low in the evening, your shadow might be nearly the same size as you are if it is on a wall but much bigger if it is across the ground.