What does it mean "noble grape" ?

Noble grapes are any grapes traditionally associated with the highest quality wines. Noble grapes are said to retain their character no matter where they are planted. This concept is not as common today, partly because of the proliferation of hybrid grape varieties, and partly because some critics feel that it unfairly prioritizes varieties grown within France. Historically speaking, the noble grapes comprised only six varieties. The white noble grapes were Sauvignon blanc, Riesling, and Chardonnay. The red noble grapes were Pinot noir, Cabernet Sauvignon, and Merlot.