What is the difference between and iphone 5 hard case, skin, and hard case skin?

I'm looking for a nightmare before christmas case
I was looking in amazon and i would see skin and hard case skins.
I honestly do not know the difference of a case, skin, and hard case skin in protection and cover.
Tell me if one covers the back only, front only, or both

A skin is like a sticker that you stick on your iphone a hard case is a actually a case that is hard and is not flexible a hard skin case is a hard case to

A cell phone skin is a vinyl peel able sticker, that comes many characteristic pattern designs. Sticking on cell phone's surface, to improve cell phone's default outlook. It will not be bulky. You even can't feel it when you use it.
A cell phone cover usually fits snuggly over the phone. It is usually made of silicone or hard plastic.
A cell phone case on the other hand, is more loosely fitting and is usually made from leather or nylon material.
But we usually call cell phone case and cell phone cover as one thing. They can mainly be divided into two types, hard ones and soft ones.