Legato
A curved line above or below a group of notes tells you those notes should be played legato – smoothly, with no gaps between the notes.
A slur is a legato line over a few notes which means they should not be rearticulated. For example, all the notes are played with one bow movement on a string instrument or played without tonguing each note on a wind instrument.
Listen to the two examples below to hear how the same notes sound when played normally and played legato.
No legato
Legato