Life stealing

Life Stealing (aka "vampirism") is a weapon feature. 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.