Skeletal animation is a form of 3D animation in which a skeleton made of rigid "bones" is simulated inside a model. Vertices are "enveloped" to the bones and move with them, and polygons stretch and compress to fill the "joints" in between. Moving a bone high up on a "chain" causes all of the bones below it to move in response; e.g. moving the shoulder forward causes the entire arm to swing with it.
In practice, skeletal animation allows for efficient animations to be made with relative ease for almost any jointed object that can be imagined, from humans to jellyfish to electronic machinery.
Skeletal animation is not helpful when one tries to animate unstructured objects/substances like liquids or gases, however.
Caveats in Source
Skeletal animation :