Which movement is characterized by bending the spine to the side?

Lateral flexion refers specifically to the movement of the spine or torso to the side. This action involves bending the trunk laterally, which engages the oblique muscles and allows for a range of motion that facilitates various activities such as reaching to the side or performing certain exercises.

In contrast, extension involves straightening or increasing the angle at a joint, typically moving the spine backward. Flexion is a forward bending movement, decreasing the angle between body parts, while rotation refers to the twisting movement around a central axis. Since lateral flexion is the term that accurately describes the action of bending the spine sideways, it is the correct choice for this question.