Music Packs are a Cosmetic type that was introduced in Season 2 that changes the music that is played when on the lobby, Legend selection screen and the drop music.
The Legend themed Music Packs were introduced with the Season 2 Battle Pass.
The Season themed Music Packs were introduced with the Season 4 Battle Pass.
Fortune's FavorLevel 23
The Event themed Music Packs were introduced with the Iron Crown Collection Event.
Iron Crown 120
Fight or Fright
The Old Ways