If you see the word rallentando written on a musical score, it’s there to indicate that the musician should start to progressively play at a slower pace (or tempo). Often abbreviated to ‘rall’ on a score, rallentando is Italian for ‘slowing down’ – the opposite of accelerando.
Rallentando has the same meaning as the term ritardando (often abbreviated to ‘rit’), which also means ‘delaying’ or ‘becoming slower’, so you may see one or the other featured on a musical score.
When used in the middle of a piece, rallentando is likely to be followed by the term ‘a tempo’, which indicates that the original tempo of the piece should be resumed.
Examples of rallentando
You might see rallentando used at the end of a particular phrase or section of music, as this can help to signal an imminent change – it may be used to introduce a different tempo or a change in key, for example.
Rallentando is also often used at the end of a piece, to help bring the music to a gentle, rolling stop, rather than an abrupt halt.
One example of a piece that uses rallentando in these ways is César Franck’s Les Plaintes d’une Poupée (The Complaints of a Doll). Franck uses rallentando to introduce a change of key from G major to G minor, as well as to bring the whole piece to a close.