Invocations of the Scourge is a book found in the Chamber of the Guardian of Dalaran during the quest  Dabbling in the Demonic.
Invocations of the Scourge
<Levia has marked a page in this book detailing powerful death runes. One of these runes is drawn in the ritual circle>
These are various runes used by the scourge to empower their death magic rituals. Of these, one of the most powerful is Taam - the mark of the Lich.
It is used in the creation of Aberrations and Bone Golems, but can be employed in many rituals requiring powerful death magic.