A nectarine is a fuzzless variety of peach. It is NOT a cross between a peach and a plum. Fuzziness is a dominant trait of peaches. Occasionally when peach trees are crossed or even self pollinated they will produce some fruit whose seeds will grow into nectarine trees and others which will be peach trees. Nectarines will sometimes appear on peach trees, and peaches sometimes appear on nectarine trees!