BoA's = Bind on Account items.
Before the current patch, you use to earn Stone Keeper's Shards from killing bosses when your faction held Wintergrasp. With said Shards, you could purchase BoA gear. The shoulder & chest BoA items each provide 10% bonus experience, and then if you get the BoA weapons, they make any low-level character extremely OP.
Put it this way; with the BoA shoulders, chest, staff and 2 trinkets, I could solo the instance Wailing Caverns at level 20. AND I'm a warlock LOL.
They make levelling a fair bit quicker and you are really over-powered. My warlock has 135+ spell power at level 21 haha.