A tune in
traditional music is distinct from a
song: A tune is
instrumental only, whereas a song is
sung and possibly
accompanied by
instruments.
Interestingly, the ballad, while leaning towards a song in meaning, can include an instrumental air, usually a solo piece. This is what you put in-between the tunes not to get a permanent imprint of the diddly-diddly of fast reels and jigs in Irish traditional music.