The flute is a special move for bards. They can only play this song and only if they are the last one standing in the raid. They are invincible for the entire song but unable to act. It will generate a new tome called Bard Tears and can be traded or Poetics... because as an outsider looking in SE seems to hate BRDs as much as they hate PLDs.

https://www.youtube.com/watch?v=gn88yXLX08k