This document defines animation and explores its fundamental properties. Animation involves presenting still images in a way that creates an illusion of motion in the viewer's mind, as the human eye can retain an after-image for a fraction of a second to perceive motion from a sequence of slightly different pictures shown at a certain rate. Unlike live-action cinema, which captures real motion, animation creates motion that does not physically exist by lining up still pictures. While some see animation as a variety of cinema, others view it as an independent art form with its own language and properties based on creating illusions of motion through manipulation of images.