Abnormal elevation of body temperature, usually as a result of a pathologic process.

Fever or pyrexia in humans is a symptom of an anti-infection defense mechanism that appears with body temperature exceeding the normal range due to an increase in the body's temperature set point in the hypothalamus. There is no single agreed-upon upper limit for normal temperature: sources use values ranging between 37.2 and 38.3 °C (99.0 and 100.9 °F) in humans. The increase in set point triggers increased muscle contractions and causes a feeling of cold or chills...