What exactly is a white head?

If you are referring to a skin lesion, that means an acne like lesion that can be treated with improved skin care, and oral tetracycline. It is not a serious problem in most instances. there is also a lesion similar called a milia, which is entrapped epithelium from your skin.

A white head is a kind of pimple called a closed comedone, and to differentiate it from a blackhead, or open comedone where the sebaceous plug is exposed to the open air and oxidizes a black color. Treat both of these gently to avoid scarring.