All music, fast or slow, has rhythm. Rhythm is the steady flow of music in time.
Most music is kept going by a regular pulse which is called the beat. It keeps going steadily under the music, like the heartbeat or the ticking of a clock.
“Tempo” refers to how fast or slow the rhythm is. Here are the most common musical tempos, and they are expressed by using Italian words:
Lento Very slow
Andante Moderately slow
Moderato Medium fast
Allegretto A little faster than moderato
Presto Very fast
Ritardando Gradually slower
Accelerando Gradually faster
A composer uses tempo to indicate mood. Music with an adagio tempo is usually gentle. Music with an allegro tempo often is happy and cheerful. Music with a presto tempo gives the listener a sense of lively action.
“Dynamics” is the term for describing different levels of loudness.
Composers indicate the dynamics they want by using Italian words:
Pianissimo (pp) Very soft
Piano (p) Soft
Mezzo piano (mp) Medium soft
Mezzo forte (mf) Medium loud
Forte (f) Loud
Fortissimo (ff) Very loud
Crescendo (cresc.) Gradually louder
Decrescendo (decresc.) Gradually softer
The composer also must think about how loudly or softly each instrument should be played.