Alright, so you have some kind of vague idea about what a Battleground is. Basically, Battlegrounds are where players go to consensually bash each others brains out. Or fry them. Or freeze them. These instances are designed for players to enjoy PvP, get a bit of honor and, if you're not already at max level, some experience. In the future, Blizzard has revealed plans to make the Battlegrounds even more like instances or dungeons by hinting at possible actual loot rewards.
Blizzard Entertainment has announced the opening of beta registrations for “World of Warcraft: The War Within,” inviting players to explore new subterranean worlds beneath Azeroth.
Danish from eXputer: "Despite Blizzard's attempt to give a fresh new spin to World of Warcraft, some fans still seem to be stuck in the past."
HG writes: "Blizzard is usually pretty bad at keeping secrets, but the company somehow managed to keep this one under wraps until now. Plunderstorm is a special limited-time event that’s basically World of Warcraft’s take on the Battle Royale genre."