What is a sudden involuntary contraction of a muscle called?

The term that accurately describes a sudden involuntary contraction of a muscle is "spasm." Muscle spasms occur when a muscle contracts uncontrollably, leading to a temporary tightening or stiffness. This can result in discomfort or pain. Spasms can happen in any muscle in the body and are often caused by factors such as overuse, dehydration, or muscle fatigue.

While a cramp is also a type of muscle contraction, it typically refers to a painful condition that often results from prolonged use or dehydration and can last longer than a spasm. A twitch, on the other hand, usually refers to a minor, involuntary muscle contraction that may not be painful and often goes unnoticed, unlike a spasm. The term "contraction" is more general and refers to the process of muscle shortening in response to stimulation, rather than specifically denoting an involuntary episode. Thus, "spasm" is the most precise term to describe the sudden and involuntary nature of the contraction in question.