A lip or liplike structure, especially one of the two pairs of folds of skin at the opening of the vulva. The labium is an important part of the female reproductive anatomy.
In entomology, the lower lip of an insect, formed by the fusion of the second pair of maxillae. The labium of the insect helps it manipulate food.
In botany, either lip of a bilabiate corolla, especially the often enlarged lower lip of an orchid flower. The distinctive lower labium of the orchid guides pollinators toward the nectar.