A "charley horse" is a common term for a muscle cramp, typically occurring in the leg. It involves a sudden, involuntary contraction of a muscle, often causing sharp pain. These cramps can happen during physical activity, at rest, or even during sleep. The exact cause of charley horses can vary, but they are often linked to dehydration, muscle fatigue, or electrolyte imbalances. Stretching and massaging the affected muscle can help relieve the discomfort. Staying hydrated and maintaining a balanced diet may also reduce the frequency of these cramps.