There are three types of nectarines: freestone, clingstone, and torrefied.
Free-stone nectarines have a loose outer skin that can be peeled off. The flesh inside is usually very juicy and contains small seeds. Clingstone nectarines have a firm, hard outer layer that adheres to the flesh inside. The juice and flavor are usually much better than free-stone nectarines because the seeds are removed. Torrefied nectarines are just like clingstone nectarines, but they have been oven-dried so the outer layer can be easily torn away.