Rigging
Building a skeleton of bones with controls and constraints so an animator can pose and deform a 3D model without touching its vertices directly.
The rig is the control layer bolted onto a model: a skeleton of bones, plus the handles, constraints and driver nodes an animator actually manipulates. It decides where the joints sit and what motion is allowed, while binding the mesh vertices to the bones is the job of skinning. A good rig hides the complexity behind a handful of legible controls — grab one foot, not thirty bones.
The term comes from film and VFX pipelines in tools like Maya and Blender and carried straight into games. Facial rigs are often built from blend shapes, while body rigs lean on inverse kinematics so a foot can be planted and the leg solved backwards. Rigging is the step between a static model and anything you can animate at all.