A
spasm is a sudden, involuntary
contraction of a
muscle, a group of muscles, or a hollow
organ such as a
heart, or a similarly sudden contraction of an
orifice. It most commonly refers to a
muscle cramp which is often accompanied by a sudden burst of
pain, but is usually harmless and ceases after a few minutes. There are a variety of other causes of involuntary muscle contractions, which may be more serious, depending on the cause.