A grape variety that is the product of crossing European vinifera vines with North American vines (e.g. Marechal Foch, Baco Noir, Vidal, Seyval Blanc). Tend to be winter-hardy and resistant to disease and phylloxera, usually without a "foxy" taste or aroma. Sometimes incorrectly called American Hybrid, they have unfortunately fallen into disfavour in some circles.
No doubt from the earliest days of agriculture (c. 10,000 BCE) growers have used nature's proclivities to improve upon plant varieties. The produce we see on store shelves today rarely resembles the plants or fruits that existed millennia ago. (The modern carrot, for example, at one time more resembled a dandelion root.) The main tool that growers use is crossbreeding: using the pollen from one plant to fertilise another of the same or a similar species.
When Europeans "discovered" North America, they were impressed with the vigour of American grapevines. On the downside, the wines they produced were not up to the standard that existed in Europe. Attempts to grow European vines in North America failed due to the many pests and diseases against which the vines had no defences. When North American vines were planted in Europe, the wines they produced were no better than what the native soil produced.(*) So breeders began experimenting by crossing North American grapes with European grapes.
Breeding grapes is a long, painstaking and mostly disappointing process. Many breeders create hundreds of new hybrid varieties, but only see a handful that produced a decent wine. Francois Baco is a perfect example. He created more than 2000 new varieties, but only Baco Blanc and Baco Noir gained any popularity, and now Baco Blanc has all but disappeared from vineyards.
French hybrid grapes have many advantages. They are mostly immune to North American diseases, which makes them ideal for regions where diseases and phyloxerra are a problem. They tend to be cold hardy, making them ideal in marginal regions -- some parts of Canada, the middle states of the US and Great Britain, among others. They require fewer chemicals in the vineyard making them more economical and more environmentally friendly. Their rootstocks are also valuable and are used in almost every wine region where vinifera scions are grafted onto the more rugged Americanized roots. To add insult to injury, many winemakers and even wine authorities are banning hybrid grapes from vineyards, which is unfortunate. While the taste profiles of some hybrid grapes are not really mainstream, some of them create better wine and at a lower cost than many highly touted vinifera vines. And as our various climates continue to change, the lowly hybrid grape could make a comeback!
* These experiments also introduced phyloxerra to Europe.