labium

Labium is a term from Latin meaning lip, used in biology to describe lip-like structures in a variety of organisms. In anatomy and medicine, it most commonly appears in reference to the lips of the mouth or to lip-like features associated with reproductive or sensory organs. The plural form labia is widely used for some of these structures, most notably the external female genital lips.

In human anatomy, the labia refer to the external female genitalia, divided into two pairs: the labia majora (outer lips) and the labia minora (inner lips). The labia majora are typically larger, outer folds that enclose and protect the more delicate inner structures, while the labia minora are thinner, hairless folds that surround the openings to the vagina and urethra. The appearance of the labia can vary considerably among individuals and throughout life, influenced by hormonal changes, age, and genetics. The labia are richly supplied with nerves and glands and participate in sexual function and protection of the internal genital tract.

In insects, the labium is one of the mouthparts and forms the lower lip. It is typically a composite structure derived from fused maxillary parts and often bears labial palps at its distal end. The labium helps manipulate food and can be simplified or highly specialized in different orders; in some species it contributes to forming a feeding tube or rostrum.

In botany, the term labium can describe a lip-like portion of a corolla, particularly the lower lip in bilabiate flowers. The more specific term labellum is commonly used for the orchid lip, while labium is encountered in some botanical contexts to indicate a lip-like floral structure.