flexion

Flexion usually means the act of bending a body part at a joint, such as your elbow, knee, wrist, or fingers. In simple terms, it is the movement that makes the angle between two parts smaller. Think about lifting your hand toward your shoulder in a curl or bending your knee to climb stairs. You will often see this word in anatomy, medicine, physical therapy, and sports science.

It can also appear in grammar, where it means a change in the form of a word to show things like tense, number, case, or person. This use is less common in everyday speech, but you may meet it in language study. The word comes from the Latin flectere, meaning "to bend."

Flexion refers to a bending movement, most often in the body. In anatomy and kinesiology, it means decreasing the angle between two body parts. When you bend your elbow, knee, wrist, neck, or fingers, that is flexion. A doctor, trainer, or physical therapist may use the word when talking about how well a joint moves or whether movement is painful or limited. The opposite movement is usually called extension, which straightens the joint.

This is the most common use of the word today, especially in health and movement contexts. You might hear about spinal flexion, hip flexion, or flexion of the fingers. In each case, the idea is the same: something bends inward or closes the angle at a joint. The word comes from the Latin flectere, meaning "to bend."

There is also a language-related use. In grammar and linguistics, flexion can mean a change in the form of a word to show its role or meaning in a sentence. For example, a word may change form to mark tense, plural, or case. In this sense, flexion is closely related to inflection, and in many contexts the two words overlap.

You may also find the word in older or more technical writing for a bend or folding movement in general, but that use is less central than the body and grammar senses. So if you see flexion, think first of a joint bending, and then, in language study, of a word changing its form.