Damage Over Time

Damage Over Time is also known as DoT

As the the term suggests, it is damage applied over successive seconds as opposed to one single burst. Generally used to simulate, burning or poisoning.

For example:

Rank 15 Ring of Fire-

"...burns up to 12 enemies by sending out a wave of fire bolts in a 360 degree radius. Each bolt deals between 200 to 1402 Fire Damage and has a chance to inflict between 327 to 1854 Fire Damage over 3 seconds."

The 200 to 1402 would be instantaneous damage.

The 327 to 1854 over 3 seconds is Damage Over Time, which works out to 109 to 618 damage every second for 3 seconds.

See DoT Stacking for additional information.