User blog comment:FairyRaven/Fairy Tail Chapter 353: Exorcism, Review and Commentary/@comment-11966702-20130927160440

E.N.D.? That should stands for Eternal Night for Dragons = an ultimate magic for wiping out all the dragons.. That's why a dragon such as Atlas Flames refer the magic as the most sinister in Zeref's book.. (Just a wild guess..)