Soft body
A body that deforms under force instead of holding a fixed shape — cloth, jelly, rubber — the opposite of a rigid body.
Where a rigid body moves and rotates but never bends, a soft body squashes and wobbles. The cheap classic model is a mesh of point masses joined by springs or distance constraints, stepped with Verlet integration and relaxed each frame — the recipe behind most cloth and rope in games. Fancier engines reach for position-based dynamics or the finite element method for believable flesh and rubber.
The price is that a soft body has far more state to track and solve than a rigid one, so games choose their deformables deliberately rather than making everything squishy.