Necromantic sorcery is the study and implementation of spells that deal with the dead and the undead. It is considered an evil branch of magic and necromancers are highly frowned upon by the true sorcerers of Faerun who feel that delving so far into the dangers of the Black Arts can bode no good to the Realms.
It is this very aura of "forbidden fruit" that compels many to take up this arcane study of the Undead.
Although their spells are unique, Necromancers do not have the heavy offensive spell capabilities that other magic users do. Instead, they rely on their undead to dole out, and take the heat of battle.
It is widely rumored that some Necromancers become so powerful that they are able to harness the Dark energies and transcend their OWN boundries between life and death -- effectively transforming themselves into fearsome and immensely powerful liches.