there are Several depending on context:
piu mosso = more motion. gen. interpreted as being 'faster'
accelerando = getting faster (but gradually)
doppio movimento = doubly fast.
a change in metronome marking from a slower M.M to a faster M.M.
or simply, "Faster".
Also, a sudden jump to another tempo can be denoted with either a simple tempo direction (allegro or sub. allegro meaning "suddenly faster", etc.) or just a metronome marking indicating the new tempo. It depends on whether you want a specific tempo or for the player (or conductor) to feel a faster tempo by virtue of what was just happening.