What is the medical term for a violent, involuntary contraction of muscles?

The medical term for a violent, involuntary contraction of muscles is "convulsion." This term specifically describes a sudden, uncontrolled electrical disturbance in the brain that can cause changes in behavior, movements, sensations, or consciousness. Convulsions are often associated with conditions such as epilepsy, where the brain experiences irregular activity that leads to these forceful muscle contractions.

While the other terms relate to muscle activity, they do not encapsulate the violent and involuntary nature described in the question as effectively as "convulsion." For instance, a seizure is a broader term that includes convulsions, but it encompasses various forms of abnormal brain activity beyond just the muscle contractions. A tremor refers to a rhythmic shaking movement, usually involving a specific part of the body, and a spasm generally refers to a sudden involuntary muscle contraction but lacks the intensity and violent nature characteristic of a convulsion. Hence, "convulsion" is the most precise term in this context.