A medical student is an individual enrolled in medical school who is training to become a doctor. They have already completed four years of college, and often two years of pre-clinical classroom work. Their work in hospitals is limited to training. They do not prescribe or diagnose without direct supervision from a resident, fellow, or attending physician. In many hospitals, medical students are required to wear short white coats to distinguish them from other physicians.
In teaching hospitals, these are often the people you see first.