An abnormal facial configuration in which one or both jaws project forward.

It may be real or imaginary, depending on anatomic or physical and developmental factors.

Real prognathism may exist when both the mandible (lower jawbone) and the maxilla (upper jawbone) increase in length or when the maxillary length is normal and the mandibular length increases excessively.

Imaginary prognathism may exist when the maxilla is underdeveloped and the mandibular length is normal