Cramps were a mild condition wherein muscles involuntarily contracted. Cramps were an unpleasant sensation and were often the result of stress or strain on the muscles in question. The muscles could also be part of an autonomous muscular system, such as the stomach.
When trying to get in to a secure section of San Francisco Mercy hospital, Doctor Leonard McCoy baffled a security guard by describing doctor Gillian Taylor's condition as "immediate post-prandal upper-abdominal distension", which he later described to Admiral Kirk as the medical description of cramps. (Star Trek IV: The Voyage Home)
While on board the USS Prometheus in 2374, The Doctor told the Romulans in control of the vessel that the Terothka virus they supposedly were exposed to might give them unbearable stomach cramps, though the rash might be worse. (VOY: "Message in a Bottle")