The Flame Deflector is a temporary shield from fire damage. It can be used from inventory and does not have to take up an equipment slot like a trinket. The Deflector can be used by non-engineers.
The Deflector does not stack with Mage's Fire Ward spell or with Fire Protection Potions (regular or Greater).
Background
This section concerns content exclusive to the Warcraft RPG, and thus is not necessarily canon.
A percentage of magi are, at heart, closet pyromaniacs. Not only do they call down fire on their enemies during battle, they find any other excuse to burn something down. A dwarven tinker adventurer developed the flame deflector because he was tired of getting caught in the collateral damage caused by his associate's overzealous spellcasting.
The flame deflector is a compact device fitted around the neck like a thick brace. Cooling elements housed in its thick pads sit on the wearer's shoulders, held there by straps slung under the armpits.[1]
Patch changes
Patch 1.4.0 (2005-05-05): Flame Deflector now does an elemental damage absorb rather than a resistance increase.