Scientists in the lab of Giacomo Rizzolatti at the university of Parma in Italy (were studying) macaque monkeys to see how their neurons were firing. They began to notice that some neurons were firing in exactly the same pattern whether the monkey was picking up a piece of food and eating it, or was watching a human or another monkey pick up a piece of food to eat. It didn’t matter whether the monkey was performing the activity or watching it. The neural response was the same.
— Cathy Davidson, Now You See It

Motion: voluntary and reflex movement, movement adjustments, and movement plans. (Patestas, 171) A change in location or position. (NCIt)

The act, process, or result of passing from one place or position to another. Encompasses "locomotion" (and) also changes of the position of the whole body or any of its parts. Movement may be used with reference to humans, vertebrate and invertebrate animals, and microorganisms. The physical activity of a human or an animal as a behavioral phenomenon. (MeSH) Verb - 'moving.' Also referred to as 'movement' and 'motility.'

Locomotion: the action or power on the part of an organism, or vehicle, of moving from place to place. (Oxford) Movement restricted to the passing of the whole body from one place to another. (MeSH)

Motor: designating or pertaining to neurons or nerve fibers which initiate or convey impulses resulting in an action, especially muscular contraction. Any part of the central nervous system which has a motor function. (Oxford) Adjective - 'motoric.'

Motor Imagery: the process of imagining a movement. As far as the “primary motor cortex” is concerned, executed and imagined movements are almost identical. (Blakeslee, 61) (Also), motor cells could fire merely at the perception of somebody else's actions, with no motor action involved at all. (Iacoboni, 11) Also referred to as ‘kinesthetic imagery.’

Vestibular System: the sensory organs for the "balance" system. The balance system gives us our sense of orientation in space. When running, the vestibular apparatus sends messages to our brain, telling it the speed and direction in which we are running. If we move our heads forward, our brains tell an appropriate segment of our bodies to adjust, unconsciously, so that we can offset that change in our center of gravity and maintain our balance. (Doidge, 3) Vestibular structures are equipped with two groups of receptors, one detects angular acceleration (rotational movement) of the the head, and the other detects spatial orientation of the head in space. (Patestas, 319) Damage here can result in difficulty standing and worse – a sense of falling endlessly like into a bottomless pit as happened with patient Cheryl Schiltz.’ Experiments with 'Cheryl' by Dr. Paul Bach-y-Rita showed “neuroplasticity” could be facilitated with man-made devices. (Doidge, 8)

Balance: the maintenance of a stable, upright body position. (NCIt) Mediates the special functions of posture maintenance, muscle tone, equilibrium, and coordination of head and eye movements. Transmits sensory information to the brain regarding the position of the body and spatial orientation. (Patestas, 318)

Vestibular Apparatus: an oval, bony chamber of the inner ear. (MeSH) The sensory apparatus … including the "semicircular canals.” (Patestas, 319) The cavity of the (inner ear) that contains the organs of balance. (OxfordMed) Also referred to as ‘labyrinth vestibule.’

Semicircular Canals: three semicircular canals in the inner ear that tell us when we are upright and how gravity is affecting our bodies. One canal directs movement in the horizontal plane, another in the vertical plane, and another when we are moving forward or backward. The canals contain little hairs in a fluid bath. When we move our head, the fluid stirs the hairs, which send a signal to our brains telling us that we have increased our velocity in a particular direction. (Doidge, 3)

Vestibular Nuclei: the four cellular masses in the floor of the “fourth ventricle” giving rise to a widely dispersed special sensory system. (MeSH) A specialized clump of neurons in our brain that receives signals from the vestibular apparatus, processes them, and then sends commands to our muscles to adjust themselves. (Doidge, 3)

Vestibular Sense: the technical name for the sense of balance, or sense of equilibrium. (Hockenbury, 104)