The Thunder Shield is a shieldweapon which has a lower damage reduction on block than most other shields and deals electric DPS when held up or in a radius around the player after a successful parry. Reusing the shield while it's charged will discharge the energy, dealing shock damage and stunning nearby enemies. This item is exclusive to the Rise of the Giant DLC.
Thunder Shield worked differently prior to v1.3. It wasn't able to deal area damage or discharge the energy, but successful parries increased the DPS by ~2.7 times.