Life stealing

Life Stealing (a.k.a. "Vampirism") moves health from the target to the attacker. It is not considered damage and will not trigger or be affected by any skill/equipments effects related to damage.

Life Stealing Skills
The following skills do life stealing:
 * Necromancer
 * Vampiric Gaze
 * Vampiric Touch
 * Unholy Feast
 * Soul Leech
 * Mark of Subversion
 * Barbed Signet
 * Order of the Vampire
 * Shadow Strike
 * Insidious Parasite
 * Feast of Corruption
 * Taste of Death (Minion)
 * Soul Feast (Corpse)

Vampiric Weapons
"Vampiric" is a weapon feature, added by a "prefix" weapon upgrade.

It means that every time the weapon hits a foe on top of the normal damage it will steal the specified amount of health from the foe and heal the attacker for the same amount.

To balance the Life Stealing, vampiric weapons always come with -1 Health Regeneration, which continues as long as you have the weapon equipped, so while not in combat it's advisable to switch to another Weapon Set.