SuperTuscan Blend refers to wines which feature a significant Sangiovese component combined with grapes not traditionally associated with Italy like Merlot or Cabernet Sauvignon. This separates it from "Sangiovese blend" which is used for wines which are predominantly Sangiovese and combined with traditional Italian varieties. There is often confusion as many wines most famous associated with the term "Super Tuscan" like Sassicaia, Masseto and Ornellaia have no Sangiovese and are properly linked to 'Red Bordeaux Blend.'
In fact, Super Tuscan was a term coined to refer specifically to wines such as Sassicaia and Tignanello. These were wines that "fell out" of the official DOCG classification of Italian wines because they either contained grapes not permitted (international varietals such as cabernet sauvignon or merlot,) were aged differently (I.e. in barrique) or were 100% sangiovese - which was not permitted at the time for Chianti (E.g. Fontodi Flaccianello.) Forced to be classified as simply "Vina di Tavola" these wines nontheless quickly found favour in international markets and comanded prices above the highest quality DOCG Chianti Classico & Brunello di Montalcino wines at the time. The wine industry and press began to refer to these wines as SuperTuscans because of their popularity and quality, but also because of the prices they commanded. Subsequently, the Italian authorities, under the Goria Law 1992, redrew the classifications, and included the category IGT (Indicazione Geografica Tipica) to classify the SuperTuscans.