Which movement is characterized by a decrease in the angle between two body parts?

Flexion is the movement that results in a decrease in the angle between two body parts. This term is commonly used in anatomical contexts to describe actions such as bending a joint. For example, when you bend your elbow, bringing your forearm closer to your upper arm, you are performing flexion at the elbow joint. Similarly, bending your knee or tilting your head forward are other instances of flexion.

In contrast, extension increases the angle between body parts, such as straightening your knee or lifting your arm to the side. Abduction refers to moving a limb away from the midline of the body, while adduction involves moving it toward the midline. Hence, flexion is distinctly characterized by the action of reducing the angle, making it the correct answer to this question.