The Ghoul summoned by your Raise Dead spell is considered a pet under your control. Unlike normal Death Knight Ghouls, your pet does not have a limited duration. Also reduces the cooldown of Raise Dead by 60 sec.
Patch 4.0.1 (2010-10-12): Changed from a tier 6 talent to a passive specialization for Unholy death knights. Now also reduces cooldown of Raise Dead by 60 sec.
Patch 3.1.0 (2009-04-14): Now also reduces the cooldown on Raise Dead by 60 sec.