The upper lip is the part of the mouth located above the lower lip and below the nose. It plays a crucial role in facial expressions, speech, and eating. The upper lip is made up of skin, muscle, and connective tissue, and it contains various sensory receptors that help detect touch and temperature. In humans, the upper lip is often associated with aesthetic features, such as the shape and fullness, which can vary widely among individuals. It also serves as a boundary for the philtrum, the vertical groove that runs from the nose to the upper lip, contributing to facial symmetry and expression.