Concerning a music composition or passage to be played slowly: Mary's voice teacher told her to sing the song in a largo manner, that meant to be sung in a lento way.

Referring to how a piece of music is to be played in a grave way: The soloist accidentally played her piece allegro, and not largo with dignity, like it was supposed to be!

A piece of music, particularly a part of a longer composition,, that is played slowly: The conductor told his orchestra that the largo had to be played gravely and unhurriedly.