Carols are a type of song in Final Fantasy XI. Because they are high-level songs, they are available only to Bards. There are a total of eight Carols, each one corresponding to one of the eight elements: Earth, Wind, Water, Fire, Ice, Thunder, Light, and Dark.
Despite their high level, Carols offer relatively similar protection versus each of these elemental forces as White Magic Barstonra, Baraero, Barwatera, Barfira, Barblizzara, or Barthundra. Their considerable advantage is probably their ability to guard against Light and Dark elements and that they actually stack with Bar-type spells to provide even greater defense. Even considering that, their use is relatively limited to only certain circumstances.