Final answer:
Extension is the term that describes the increase in the angle of a joint, straightening it. Abduction moves a limb away from the body, adduction brings it toward the body, and circumduction involves a circular motion.
Step-by-step explanation:
The term that increases the angle of the joint is extension. Flexion decreases the angle between bones, as seen when bending a joint. In contrast, extension is the movement that increases the angle between bones, straightening the joint. For example, when you straighten your arm at the elbow or straighten your leg at the knee, you are extending the joint.
Additionally, abduction is the movement of a limb or part away from the midline or center of the body, and adduction brings it closer to the midline. Circumduction is a circular movement combining flexion, abduction, extension, and adduction movements.