A DoT or Damage over Time is a type of skill that will do initial damage to an opponent, and continue to inflict damage over a specified length of time. Spiritmasters, Sorcerers, and Clerics commonly use this type of skill. The debuff can be removed with an item such as a 
<Greater Healing Potion>, or 
<Healing Root> or with a spell such as 
<Dispel I>.
Strategically, a DoT skill can be used to pull an enemy from a congested area to one where they can be more easily killed. If there are social NPCs which pull with the desired target, the others will drop as the player runs to the safer spot, while the DoT maintains damage and therefore aggro from the target. The DoT might need to be recast to maintain it while pulling the target.