Muscles act by moving joints. Thus, the same terminology can be applied to both muscle actions and joint movements. Most joint movements are described by opposing terms (directions). One set of muscles moves a joint in one direction; another set of muscles moves the same joint in the opposite direction.

Most joints in the body function as "hinge" joints, meaning they move (extend/flex) in one plane. Ball and socket joints (e.g., the hip joint) are capable of circumduction (circular motion). Limbs as a whole are capable of rotation (supination/pronation) and movement away from (abduction) and toward (adduction) the body. The head extends/flexes (YES motion) at the occipital-atlantal joint and rotates (NO motion) at the atlantal-axial joint. The spine (vertebral column) extends dorsally and flexes ventrally.

Extension - Flexion:
Extend -- increase the angle formed by a hinge joint.
Flex -- decrease the angle formed by a hinge joint.

Abduction - Adduction:
Abduct -- move the limb away from the body (midline).
Adduct -- move the limb toward the body (midline).

Supination - Pronation:
Supinate -- rotate the thoracic limb so the dorsum of the manus is turned laterally (outward rotation is preferred for the pelvic limb).
Pronate -- rotate the thoracic limb so the dorsum of the manus is turned medially (inward rotation is preferred for the pelvic limb).