Spellstorm

Spellstorm refers to a type of magic wielded by Druids. It means, alike Frostfire, that a spell can do either Arcane or Nature spell damage. Spellstorm is special as it combines the strengths of these two elements - if an enemy is invulnerable to Arcane, it will deal Nature damage and vice versa. It also works around resistances and absorption effects in the same manner, thus evading a mage's Mage Ward, but not the warlock's Nether Ward, but too the warlock's Nether Protection. The only spell that uses it so far is Starsurge, and the power of the spellstorm damage here is that it can take advantage of both the Eclipse effects that Balance Druids use.

History
The first and only spell that uses Spellstorm damage, Starsurge, was introduced in patch 4.0.1 which prepared for Cataclysm.