Poison Damage is a type of damage in Titan Quest. It is reduced by Poison Resistance. The Rogue Mastery has various skills dedicated to this type of damage.
Poison Damage is almost exclusively dealt as damage over time (DoT). It's default base duration is 6.0 seconds, making poison the 'slowest' killer of all damage over time types. Poison is not considered an Elemental Damage.
Unlike the Elemental Damage types (Fire Damage, Cold Damage, Lightning Damage) or Vitality Damage, Poison Damage receives no bonuses from any of the attributes and it's effectiveness can only be increased via skills and items.