The BH is a bounty hunter quest. You get it from the NPC head hunter.
The Head Hunter is an NPC that gives the Bounty Hunter quests (or "BH" for short), which involves the killing of up to three bosses each day. The Head Hunter is located in the center of Archosaur (554, 653), on the East side of the platform with the Warsoul Spirit. Characters level 40 or higher are able to access these Daily Quests.
A few other bits of information:
* He offers a different bounty to each level range (40-49, 50-59, etc.).
* Rewards also vary depending on your level.
* You can take the quest several times each day - up to three for levels 40-90, up to twice for levels 90+.
o One of the rewards for completing the first bounty in a day is a Bounty Order allowing you to take the second, etc..
o The Bounty Order only lasts 30 minutes, so take the new quest right away.
o The higher the Bounty Hunter number (I, II, or III), the lower the rewards.
