Tempo is the Italian word for time, and it is the word that musicians use to describe the speed of a song. Tempo can be measured in beats per minute (BPM) or indicated by any of the following words:
   
We use all of these words, and more, to describe different tempos because tempo is a very important expressive aspect of music. We tend to associate slow tempos with somber, serious feelings. Faster, livelier tempos can indicate happiness.

A lot of contemporary music – especially dance tracks – maintains a consistent tempo throughout. (In fact, dance DJs carefully match songs with the same BPM so that the dancers don’t stop grooving!) But changes in tempo can be very interesting and expressive – and we have Italian words for those changes, too: