Damage Over Time
Damage Over Time, often abbreviated DoT, refers to any of several detrimental status effects or the spells/abilities which inflict them, where damage is done to the affected target in small amounts at set time intervals (often referred to as ticks) for a certain duration. They are often highly desirable on enemy targets to gradually lower their HP while at the same time not causing the high level of Enmity which would be caused by doing the same amount of damage all at once (Commonly referred to as a "Nuke".
That said, players need to be careful of DoT effects, such as Poison, both in their use and avoidance of being affected by them. DoT effects can K.O. a player not watching their HP level, and a DoT effect on an enemy or player will normally prevent them from being put to Sleep.