Squash and stretch
Animation is the change of a value over a period of time. For example by changing the y position of a ball it can be made to bounce up and down. Then by changing the x and z scale it can squash as it hit the ground. The change in position can be visualized with a curve by putting the time on the x axis of the graph and the position of the ball on the y axis. To animate the ball we select where the ball should be at the key points of the animation and the code can then interpolate the position between these key points.
Animation Compression TOC - 2016
New Animation System!!
Skinned mesh support and animations
Better animation control through scripting
Skeletal Animation Part 2: Animating Joints
Towards Skeletal Animation Support
Vertex animation textures, beanbags and boneless animations.