Euphoria Motion Synthesis
From the official euphoria page:
With euphoria, animations are not canned but are generated on-the-fly by the CPU as the game is played. Every tackle is your tackle, every haymaker is your haymaker.
Previously, animation data had to be manually created (through key-framing) or recorded (through motion capture). This is often expensive and laborious, and results in static, non-interactive data.
euphoria is instead based on a full simulation of a 3D character, including body, muscles and motor nervous system. This creates fully interactive animations that act and react differently every time.
Used in Grand Theft Auto IV