Burn Damage is a type of Damage over Time. It is reduced by Fire Resistance. The default duration for Burn Damage is 3.0 seconds.
Burn Damage receives no bonus from +XX% Fire Damage modifiers. It benefits from the Intelligence attribute, however. The formula to this is:
elementalDamageDV * ((intelligenceDV / 500) + 1)
This means, for every 50 points in Intelligence, Burn Damage is increased by +10%. 500 points in intelligence would add +100%.
The Earth Mastery has various skills that deal and increase Burn Damage.