Want a fast definition? Presto! Presto means suddenly, or super fast. Magicians love to yell presto! before a trick. In music, to play something presto is to play it at a very fast tempo.
Presto comes from Italian for “quickly.” Officially, presto is the second-quickest speed that music can be played (after prestissimo). To a pianist, presto means one thing, while to a magician it means another. In this case, presto still means "fast," but it refers to the speed at which an illusion is created. If you dabble in magic tricks, you might say, "Presto!" at the moment you make a rabbit disappear or turn a silk scarf into a bouquet of flowers.