Helm of the Vanquished Defender

Helm of the Vanquished Defender is a tier 5 armor token. It can be exchanged at Kelara at Shattrath's Aldor Rise or Veynna Dawnstar on the Scryer's Tier for the following items:

It can also be exchanged at Olus at the Isle of Quel'Danas for the following Season 2 PvP items:

Source
This item drops from Lady Vashj in Serpentshrine Cavern.