Jiggle physics
Procedural secondary motion on bones the animator never hand-animated — hair, ponytails, antennae, cloth — that lags behind and overshoots as the character moves.
The trick is to hang a damped spring (or a Verlet point) on the bone so it reaches for its rest pose relative to the parent but always trails a moment behind. When the character stops short, the tail keeps going forward and swings back. The simulation runs after the ordinary animation, bone by bone, and is tuned by two knobs: stiffness and damping. The technique is also called dynamic bones or spring bones.
It is cheap and gives a lot of life for the money, which made it common in fighting games and anime-styled games — the name is worn half in jest. The pitfall is stability: too much stiffness or a varying timestep makes the spring blow up, so values are clamped and the timestep kept fixed. It is related to both skeletal animation and soft bodies, but far simpler than full cloth simulation.