And that's probably because it's a hard thing to define. So let's talk about it!
To talk about art jewelry, you first have to talk about jewelry in general.
According to the Merriam-Webster dictionary, jewelry is:
jew·el·ry noun \ˈjü-əl-rē, ˈjül-rē, ˈju̇l-; ÷ˈjü-lə-rē\ : decorative objects (such as rings, necklaces, and earrings) that people wear on their body
Which is a decent definition, as far as the basics go.
So: "decorative," which assumes not functional. And "worn on the body," which means not sculptural, or freestanding.
But obviously there are different types of jewelry, because you expect different things from jewelry bought at Tiffany than you do from jewelry bought at Claire's.
Which brings us to fine jewelry and fashion jewelry.
Fine jewelry (like Tiffany, Cartier, Harry Winston, and so on) often contains precious metals, like platinum, gold, or silver. Gemstones are a staple of fine jewelry, particularly "the big three," emeralds, rubies, and sapphires. And, of course, diamonds. Engagement rings almost always fall into the realm of fine jewelry. Fine jewelry is sometimes one of a kind at the very high end, and sometimes produced in quantity.
And then there is fashion jewelry, which is another beast entirely. It is primarily not made from precious materials, although it is often made to look like it is. Plastics, imitations, and inexpensive materials are key to fashion jewelry. Fashion jewelry is trendy, and often has a limited life because of it. It also tends to be produced in massive quantities.