In the Warcraft universe, the living can be infected with a plague that turns them into undead. The undead can be killed.
My understanding of the state of undeath is that one is dead, yet some how animate, albeit it with rotting flesh. The undead seem to be alive in all ways but name. The undead can die and be resurrected, implying that they are alive.
What precisely is the state of being undead? How is it different to being alive?