Trial by Fire is a craftable set available in all armor types. When you take elemental damage, gain 7727 Resistance to that element for 4 seconds. You can only be resistant to one element at a time.
Trial by Fire is part of the Orsinium DLC. The crafting station is located in Wrothgar (Malacath Statue). You can craft any armor, weapon or jewelry of this set in any motif style you know, as long as you have 3 traits researched (per item). You can trade crafted pieces to other players. Each set item becomes bound on equip.