Hair's a protein filament that grows through the epidermis from follicles deep within the dermis. The fine, soft hair found on many nonhuman mammals's typically called fur; wool's the characteristically curly hair found on sheep and goats. Found exclusively in mammals, hair's one of the defining characteristics of the mammalian class. Although other non-mammals, especially insects, show filamentous outgrowths, these aren't considered "hair" in the scientific sense. So-called "hairs" (trichome… (More on Hairs)