Fur refers to the dense covering of hair or guard hairs found on the integument of various terrestrial vertebrates. Structurally, it is composed primarily of keratin, a durable protein that provides structural integrity. Functionally, the primary roles of fur are thermoregulation, allowing the organism to maintain stable core body temperatures by trapping insulating layers of air. Furthermore, the specific arrangement, texture, and thickness of the fur can provide camouflage, enhance sensory perception, and serve various roles in display or defense. The composition and arrangement of fur vary significantly across different taxonomic groups, reflecting diverse adaptive pressures and ecological niches.