User blog comment:Nick D Wolfwood/Manga vs Anime for canon material/@comment-3134619-20101109231508/@comment-3134619-20101110014356

'Canon' means material considered to be 'genuine', as in things the author explicitly states. The anime continued to run, even when material was not being produced, and in order to buy time until new chapters were turned out, they made their own arcs.

All in all, it is about Hoshino's original work D.Gray-Man; they aren't separate canons. The anime only came around /after/ the manga; without the manga, it wouldn't exist.

If the anime states anything that comes into conflict with what the author wrote, then the anime is not canon in that particular instance.