DoT
Damage over Time - the total damage caused over a set period of time.
The game evenly divides this total in set intervals, typically three seconds unless specified.
Dexterity and/or effects increasing casting speed (i.e. reducing your casting delay/time) can slightly reduce this interval's duration. This leads to skills capable of carrying out one more periodic hit of damage, without weakening the average damage produced periodically.
- E.g. if Slash dealt a base of 400 damage, it would be the same as saying 100 damage every 3 seconds for 12 seconds). If the interval was reduced to 2.4 seconds, Slash would deal 500 damage (100 damage every 2.4 seconds for 12 seconds).
DoT is affected by your attack (ranged attack for Hunters) for physical skills and magic for magical spells. The increase in damage is added towards the total damage, then divided into periodic damage.
Damage over Time is similar to Healing over Time except one deals damage and the other heals health.