The term ritardando is an Italian term meaning ‘gradually slowing in tempo’, and is a performance direction to indicate that the music should become gradually slower — usually at the end of a musical phrase. But as anyone familiar to music by now should have realised, there are several nuances and each type of ritardando, or rit, as you may hear it commonly referred to by time-pressed conductors and musicians (read: all of them), is different from the other.
When accompanied by Italian adverbs molto or poco, the nature of the deceleration changes: molto ritardando indicates large amounts of slowing down, and poco ritardando means to slow down a little.
A composer might use ritardando to indicate the end of a phrase or section of music, telling the performer to hold back a little or slow down to create musical ‘phrasing’. Some performers and conductors prefer the expressive freedom of a rubato, which does allow for greater autonomy. However, the precise nature of a ritardando at the end of a musical phrase makes it very clear to the conductor and performers exactly how the composer wishes the music to be performed, and is a useful starting-point for further interpretation.