DoT stands for Damage over Time. Its a common type of spell/effect in MMORPG's. In L2, the effect of the DoT doing damage to a mob does not count twords the caster of the DoT so they take no credit for the damage done to the mob. Because of this you can DoT a mob and let it rot (often meaning the time it takes for the DoT to damage a given mob). Then have the person you are power leveling come over and kill the mob with low life from the DoT. You will receve no xp for the kill, but the person you are power leveling will take full xp for the kill. Hope that helps some
