Cleft lip, also referred to as harelip, is a congenital birth defect that occurs when the upper lip doesn't form properly during fetal development. While this condition typically affects one in every 700 newborns, there are several other synonyms to refer to this medical condition, including lip schism, cheiloschisis, and labium leporinum. Some people may also refer to cleft lip as a "split lip" or "facial cleft." While the condition itself doesn't typically cause any health problems, it can cause speech, hearing, and dental issues if not corrected. Treatment for cleft lip typically involves surgical intervention to repair the lip and restore normal function and appearance.