In medicine, a symptom is a subjective description of a patient's experience, as recounted by the patient or a lay observer. "Ouch! I can't put any weight on my ankle" is a symptom, while a positive result by an examiner using the Ottawa ankle rules or an X-ray showing a fracture would be a sign.
Symptoms come from taking the patient's history, while signs are findings on physical examination or diagnostic testing. Both symptoms and signs go into a diagnosis.