A nectarine is a fuzzless variety of peach. It is NOT a cross between a peach and a plum.
Nectarines, like peaches, probably originated in China over 2,000 years ago and were cultivated in ancient Persia, Greece and Rome. They were grown in Great Britain in the late 16th or early 17th centuries, and were introduced to America by the Spanish.
The word 'nectarine' means sweet as nectar, and this is very likely the obvious origin of the name.
Today, California grows over 95% of the nectarines produced in the United States.
Peach seeds may occasionally grow into trees that bear nectarines, and nectarine seeds may grow into trees that bear either nectarines or peaches. It is not possible to know which fruit will grow on trees grown from nectarine seeds, so nectarine branches are grafted onto peach trees to guarantee a crop of nectarines.