Self-Nerfed Minstrel - What do I need to get...

Forgive my ignorance.. I've been playing this game since beta... but just returning from a long absence. The absence was caused by my frustration for never getting a "KEY" skill.. problem is, I don't remember what it was that I needed to get it.. it was something from an instance.. off a boss.. one of the early bosses I believe.

It is a somewhat common drop, and I'll never forget it.. the last time I ran the instance I PASSED on the item like an IDIOT..

Later on.. as I began raiding with my guildies I found out that this "skill" or technique is one of the most critical things that I can do as a minstrel.

Sorry for the rant.. but now that I've fallen back in love with this game and my minstrel.. I want to finally go back and get this thing...

What is it???? Can I get it off the AH??? What instance do I need to run to get it??

Sorry for my ignorance, I'm hoping my fellow Minstrels can help me out..

Thanks