A NORMAL body temperature varies, depending on the time of the day, but the norm is usually defined as 36.9°C. A fever then is simply defined as higher-than-normal body temperature.
Fever is a symptom caused by a variety of illnesses. It is usually in response to an infection or inflammation, but these are not the only causes. Other possible causes include poisons, drugs, cancer, excessive exposure to heat, abnormalities in the brain and certain diseases of the endocrine (hormonal) system.