A Bordeaux Blend, at its most basic, is any combination of those grape varieties typically used to make the red wines of Bordeaux. The phrase, which seems to have originated with British wine merchants in the 19th Century, relates as much to wines made from the blend as to the grape variety combination itself. Far from being an officially defined or legal term, it is almost never used for wine-labeling purposes (although it occasionally appears on back labels). Its equivalent in the United States is Meritage, which is not only legally defined, but also a registered trademark.
Red Bordeaux Blends are known for their powerful structure and deep flavors. Dark fruits and berries such as plum and blackcurrant are commonly used to describe the flavors of red Bordeaux, although there is an unlimited range of terms that have been ascribed to them. Tannins tend to be relatively high in these wines, giving them a firm structure.