Traditional forms of animation are filmed as stop-motion where the camera is stopped and the subject moved and then filmed again. This sequence of shots with small changes in between is linked together to create a moving image.
2-D animations have, or appear to have the physical dimensions of height and width, but are flat on the screen with no depth. 2-D forms of animation include model animation, claymation, pixilation animation, cut out animation, and drawn animation.
3-D animation is a newer form of digital based animation where the subjects can be viewed from all sides and the camera can move though the setting creating a more realistic sense of depth. 3-D animation uses the dimensions of height, width and depth.
Film Education (UK) has an excellent Primary Animation Resource.
MakeMovies offers a wealth of information about all aspects of animation production.