Other forms: rallentandos
When the instruction rallentando shows up in your sheet music, whether you're singing or playing an instrument, you should start decreasing the tempo.
Rallentando means "gradually slowing down" in Italian. It's based on the root word lente, which means "slowly," and anything ending in -ando or -endo in Italian indicates a process, or a gradual change. Ritardando also means "gradually slowing down." What's the difference between the two instructions? Rallentando usually applies when the tempo is about to change from a faster section to a slower one, whereas ritardando is used at the end of a piece, where it slows gradually to a complete stop.