Glossary
Proprioception
A robot's sense of its own body — joint angles, velocities, motor currents, gripper state.
Proprioception is the set of internal sensors that tell a robot what its own body is doing: joint angle encoders, joint velocity sensors, gripper open/close state, motor current (a proxy for force), sometimes force-torque sensors at the wrist.
The term is borrowed from biology — your proprioception is the reason you know where your hand is without looking at it. For a robot, proprioception is mostly straightforward: encoders are accurate, joint state is published at high rate, and the robot always knows the configuration of its body.
What's harder is using proprioception jointly with vision. Most modern policies include the current joint state as an input along with camera images, but learning how to weight proprioception against vision (e.g. when the camera is occluded) is non-trivial.