Medical can describe the practice of medicine, or a type of illness or injury. If bright red spots have erupted all over your arms, you probably have some sort of medical condition, and it would be wise for you to visit a doctor.
Medical comes from the Latin word mederi, meaning "to heal," which is exactly what medical professionals such as doctors and nurses are trained to do. When you arrive at your doctor's office or local emergency room complaining of various medical conditions ranging from strep throat to a sprained wrist, doctors provide the necessary medical care.