Cabernet Sauvignon is the most prolific black grape used to make red wine. The traditional home of Cabernet is in the Médoc in Bordeaux. In that region it is usually blended with Merlot (and many other grapes), and that tradition has been copied in most places growing Cabernet around the world.
Cabernet Sauvignon grapes have a very thick skin, which is important for a few different reasons. It makes the grapes very resistant to rot and insect problems, and also gives it the ability to produce high tannin wines, that can survive in the bottle for many years. Cabernet is often blended with other grape varietals because it is so high in tannins-- other grapes can help soften the tannins and make the wine more drinkable while it is young.
Cabernet wines are typically high in acid, full in body, and their classic flavor in cooler climates is of blackcurrants. In warmer climates, the flavor is often more fruit forward, tending towards black cherry. If you're tasting a cabernet sauvignon and you're not sure what kind of fruit you're tasting, but want to sound like you know what you're talking about, it's always a safe bet to say you taste black fruit and you'll almost never be wrong! As Cabernet Sauvignon wine ages, secondary characteristics like leather or animal hide are often accentuated.