A spasm is a sudden, involuntary muscle contraction that happens without you meaning to make it happen. Your muscles tighten up on their own, often quickly and unexpectedly. You might experience a spasm when a muscle in your leg or foot suddenly cramps up during the night, or when your eyelid twitches uncontrollably for a few minutes.

Spasms can be brief, lasting just a second or two, or they can persist for several minutes. Some are merely annoying, like a small twitch in your arm. Others can be quite painful, like the charley horse that wakes you from sleep with your calf muscle knotted tight. Athletes sometimes get muscle spasms during or after intense exercise, when their muscles are tired or dehydrated.

The word can also describe sudden bursts of other activities or emotions. A spasm of laughter means a sudden, uncontrollable fit of giggles. A spasm of coughing means a series of coughs that come rapidly, one after another, without pause. In each case, the idea is the same: something happening suddenly and involuntarily, beyond your conscious control.