Use the noun mane when you talk about an animal's ruff of neck hair. A male lion's mane can be very fluffy and dramatic.
A mane is a patch or growth of long hair, whether it's found on a lion or down the neck of a pony, or even on a human's head. You might stroke a horse's mane while sitting on its back, or you could compliment your friend on her beautiful mane of long blonde hair. The Old English root is manu, which comes from a Proto-Indo-European root, mon, which means "neck" or "nape of the neck."