Name for fine hair on human skin

If you really want to convey the idea of this specific type of hair without using technical terms or slang, I think fine body hair is as good as you're going to get. It's not evocative, but searching for it will show it's widely used by people who are trying to describe exactly what you're talking about.

The picture looks like vellus hair, which is the very light hair seen on children and sometimes adult women. That's what the picture looks like. You can read more information about vellus hair at Wikipedia.

The word for the hair that covers adult bodies (not including the hair on our heads) is androgenic hair. For more info, you may again refer to Wikipedia.

These are the correct terms; however, in English, we commonly use hair to refer to any hair on our body, though we sometimes distinguish that below the neck by calling it body hair. The type of hair in your picture, appearing on the face of a prepubescent boy, is also known as peach fuzz.

Interesting to note that in some languages there are two everyday words for "hair," one for that on our heads and one for that on our bodies.

The word down can be used to mean fine hair. From Dictionary.com: "a growth of soft, fine hair or the like".

I believe it is called vellus hair.

Vellus hair is short, fine, light-colored, and barely noticeable hair that develops on most of a person's body during childhood. Exceptions include the lips, the back of the ear, the palm of the hand, the sole of the foot, some external genital areas, the navel and scar tissue. The density of hair – the number of hair follicles per area of skin – varies from person to person. Each strand of vellus hair is usually less than 2 mm (1/13 inch) long and the follicle is not connected to a sebaceous gland.

HAIR LINE:

In the womb, fetuses are covered in tiny hair called lanugo. Shortly after birth, babies grow vellus, or fine, unpigmented hair, across the body.

When puberty hits, vellus hair give way to coarser terminal hair in places such as the underarms and genitals. The longer, thicker hair on scalp, eyebrows and eyelashes are also terminal.