Poison
From Diablo Wiki
Poison is one of the six damage types in Diablo II, and one of the four elemental ones.
Rather than instamtly doing damage, poison will do damage over a set period of time. This effect, known as being poisoned, can be cured with an antidote. Poison cannot kill the player, merely leave them with a single point of life. It can, however, kill a player's mercenary.
The Necromancer has many poison skills availiable to him, as does the Assassin.
Unique Monsters who posses the poison enchanted modifier, will do poison damage with each attack.
