The speed of a piece of music.
Some common Italian terms:
Accelerando – getting faster
Allegro – a relatively fast tempo
Andante – a tempo roughly equivalent to walking pace
Adagio - slow tempo, slower than andante
Moderato – a moderate tempo
Largo – slow and stately
Rallentando / Ritenuto (Rall / Rit) – getting slower
Rubato – playing rhythmically flexibly – slowing down and speeding up even though the music does not tell you to