The groove between the nose and the upper lip is called the philtrum, according to MedlinePlus. The philtrum is also called the medial cleft. Most mammals have this groove.
In many mammals, the philtrum carries moisture from the mouth to the nose pad, keeping the nose wet. When a nose is wet, it is more efficient at trapping odor particles. However, the philtrum does not have a known function in humans and is considered vestigial. Human philtrums develop in the womb at the point where the maxillary and nasomedial processes meet. When these two fetal features do not fuse properly, a cleft lip may result.