* Vellus Hair: This is short, fine, and lightly pigmented hair that covers most of the body. It's sometimes called "peach fuzz." Vellus hair doesn't have a medulla (the innermost layer of the hair shaft).
* Terminal Hair: This is thick, long, and usually darkly pigmented hair. It's found on the scalp, eyebrows, eyelashes, and, after puberty, in the armpits, pubic area, and on the face and body (depending on sex and genetics). Terminal hair has a medulla.
The key difference between the two is that vellus hair is typically shorter, finer, and lighter than terminal hair. Hormonal changes, particularly during puberty, can cause vellus hair to transform into terminal hair in certain areas of the body.