Leg cramps refer to sudden and involuntary contractions or spasms in one's leg muscles. These cramps can be quite painful, causing discomfort and sometimes even making it difficult for a person to walk. Leg cramps are usually harmless but they can occur due to various reasons such as dehydration, lack of potassium or magnesium in the body, poor blood circulation, muscle fatigue, or simply because of overexertion during physical activities. In some cases, leg cramps may also be a symptom of an underlying medical condition like multiple sclerosis or thyroid disorder.