Proprioception is one of the human senses. Rather than sensing external reality, proprioception is the sense of the orientation of one's limbs in space. This is distinct from the sense of balance. Without proprioception, we'd need to consciously watch our feet to make sure that we stay upright while walking.
Proprioception doesn't come from any specific organ, but from the nervous system as a whole. Its input comes from sensory receptors distinct from tactile receptors — nerves from inside the body rather than on the surface. Proprioceptive ability can be trained, as can any motor activity.
Learning any new motor skill involves training our proprioceptive sense. Anything that involves moving our arms or legs in a precise way without looking at them invokes it — for instance, activities such as baseball, basketball and painting.
Proprioception is known to be a distinct sense because there are cases in which the proprioceptive ability is absent in a patient. This means that proprioception uses dedicated brainware. Proprioception-disabled patients, for instance, can only walk by paying attention to where they put their feet.