Is World of Warcraft the Burning Crusade an expansion set?

Yes, it is an expansion game for World of Warcraft. This means that you must have World of Warcraft installed on your computer to install World of Warcraft the Burning Crusade(http://wow.igxe.com/). All of them need the original game in order for them to be played, though I do not know if the original games come bundled with the newest expansion packs or not, but I think that anything's possible.