The component unit of the plumage which grows from the skin (epidermis), consisting generally of a quill, shaft and two vanes of barbs (see pictures). A feather is made of practically nothing but keratin; the mechanically very strong, specialised protein product of epidermal cells, which become totally keratinised and stick together when dying off. The barbs (rami) which together make up the vane on each side of the shaft or rachis, are each provided with barbules (radii), see picture. The hooked distal barbules (pointing to the tip of the feather) of each barb catch upon the curled proximal barbules (pointing to the base) of the next more distal (to the tip) barb, and thus constitute the vane. If barbs become unhooked they can be made to engage again by stroking the feather from the base towards the tip, as is done when a bird is preening (feather maintenance). The shaft and also the barbs are mainly filled with air which replaced the dead, blown-up and fully keratinised cells during formation of the feather. Before a feather is more or less fully grown it is contained within and protected by a resistant sheath which later splits and is lost. For feather maintenance a range of highly stereotyped basic movements exist (together with associated behaviour), widely distributed throughout the Class Aves. The major ones are bathing (in water), drying, oiling, preening (cleaning with the bill) and head scratching.

Alternative forms for feather : barb, barbs, barbule, barbules, emargination, feathered, feathering, feathers, inner web, notch, outer web, shaft, vane.