Necromancy was a school of magic whose spells manipulate the power of death, unlife, and the life force. A wizard who specialized in the necromantic school was called a necromancer.
Spells involving the undead made up a large portion of this school, including animate dead and finger of death. Highly focused on the Negative Energy Plane, most spells from this school drained abilities.
This school was the one most associated with lichdom, a process that allowed the caster to live (or rather, exist) in an undead state indefinitely by securing their essence in a receptacle known as a phylactery.