1. A sudden, violent, involuntary contraction of a muscle or a group of muscles, attended by pain and interference with function, producing involuntary movement and distortion.
2. A sudden but transitory constriction of a bodily passage, canal, or orifice.

• A muscle spasm can be quite painful, with the muscle clenching tightly. A spasm of the coronary artery can cause angina.
• Spasms in various types of tissue may be caused by stress, medication, over-exercise, or other factors.

3. A brief, automatic jerking movement.
4. Sudden burst of activity: a sudden brief emotion, sensation, or action.

A muscle spasm, or muscular contraction, that causes a recently dead body to twitch or jerk: The new police recruit was startled by the cadaveric spasm he observed during the routine police investigation at the death scene."

A disorder of the facial nerve, causing involuntary spasmodic contractions of the facial muscles supplied by that nerve.

A sudden, violent, involuntary contraction or a jerky affection of the muscles of the lower extremities; such as the legs: Saltatory spasms cause patients' leg muscles to twitch or to jerk and are also known as tics.