As for a good definition. Perhaps Yoshiboy would be appropriate:
"When you animate something in a game you use these things called “bones”. They are quite similar to their human counterpart in that you move the bones as part of the animation and then the rest of the mesh follows. These bones are used because it makes animation much, much easier than if you were to just move every vertex of face individually.
There is only one downside to the use of bones in animation. It means that anything that is animated has to be “rigged” to the skeleton (collection of bones) so that the computer knows how the model reacts when the bones move.
The process of Rigging is in theory very simple. You tell the computer how much each vertex is affected by each bone in the model when the bone moves. When the vertexes are attached they will move with the bones allowing the model to be positioned and animated simply by moving a handful of bones.
In mount and blade there are only two types of models that are animated: Humans and horses. This means that overall the amount of rigging we have to do for mount and blade is very little. We only need to rig body armour and any new horses that we make."
http://forums.taleworlds.com/index.php/topic,15272.0.html
