Definition: "Squash and stretch" refers to an animation technique used to depict exaggerated animated motion. The point of squash and stretch is to make the motions larger than life, rather than more swift, realistic, and sometimes unnoticed in passing observation.
The reason it's called "squash and stretch" is because characters and objects are shown to "squash" (become distorted or flattened) when affected by weight or gravity, and "stretch" (become elongated) when affected by momentum or other forces, in ways that are (usually) impossible in reality. A key principle of squash and stretch, however, is the fact that the object/character animated retains the same volume/apparent mass; it's simply distorted into a different shape and/or configuration to give the impression of the forces acting on it.
