They are not usually meant to be played with, even though they have the term "doll" attached. The do not have to be human, or look remotely humanoid. Art dolls can be animals, mythical creatures, or even abstract.
They are usually One-Of-A-Kind (OOAK), and will often go for fine art prices. Art Dolls have avid collectors that enjoy collecting from certain artists and finding new and up-and-coming artists, or on certain themes.
Many art dolls are created of fabric, tho that is not always the case. Paperclay and polymer clays can be used for heads and hands or for the whole body. Art dolls can be created as gifts and are sometimes called "healing dolls"