Motion capture (mocap)
Recording a real performer's movement and mapping it onto a digital skeleton, instead of animating every pose by hand.
Optical mocap tracks reflective markers with a ring of synchronised cameras (Vicon is the classic system); inertial suits measure with IMU sensors and need no camera stage (Xsens); markerless mocap solves the motion straight from ordinary video with computer vision. The data is then cleaned and retargeted onto the model's skeleton, whose proportions rarely match the actor's.
The idea inherited rotoscoping's trick of tracing film frame by frame. Mortal Kombat (1992) digitised real actors into sprites, and from the mid-90s skeleton-based mocap became the default for realistic movement. Raw capture is seldom the final product — clips are cleaned, looped and blended with hand animation and inverse kinematics.