Key Frame Systems - computer animation
This method is for low-level motion control. In fact these systems comprise languages that are designed simply to produce the in-betweens from the user- given key frames.
Generally, each object in the scene is explained as a set of rigid bodies linked at the joints and along with a restricted number of degrees of freedom. Key frame systems were developed through typical animators as Walt Disney. An expert animator would design or say choreograph an animation through drawing exact intermediate frames, termed as Key frames. So the other animators would draw in-between frames.