A French drink sometimes known as wine brandy. It's made from a mixture of Cognac and fresh grape juice; the cognac stops the fermentation process, and the resulting liquid is aged in oak barrels. Depending on the varietal(s) used, Pineau may be red, white, or rose; in all cases it is sweet and potent (16-22% alcohol). In France it is usually served chilled as an aperitif with strong cheese or seared foie gras, but it makes an excellent dessert wine as well. It is used in cooking, particularly in sauces for fowl.
The French are very particular about these things, and to be known as Pineau des Charentes, the drink has to originate in the Charentes region, which also produces cognac. Something similar is made in the champagne region, but it's known as ratafia; from the Armagnac region, there's floc de Gascogne.