Which term refers to a tempo that is very fast?

The term that refers to a tempo that is very fast is "Presto." In musical terminology, Presto indicates a tempo that is faster than Allegro, which is already a brisk speed. This makes Presto one of the quickest tempo markings used in music notation, often signaling that the music should be played with great energy and speed.

Allegro, while fast, does not reach the extreme speed indicated by Presto. Andante signifies a moderate tempo, generally considered to be walking pace, which is much slower than both Allegro and Presto. Pianississimo, on the other hand, refers to a dynamic level indicating an extremely soft sound, rather than a tempo indication. Thus, Presto is the appropriate term for indicating a very fast tempo.