That means that all expansion packs up through Mists of Pandaria are now free to play through. This is being done in preparation for the upcoming release of the new expansion, Warlords of Draenor.
The Iron Tide update includes a tremendous number of changes, too many to list here without taking a few hours to work on formatting. However, the highlights of the patch include new character models for the original races (other updates for later races will be coming later), a ton of new content, changes to group finder, changes to the inventory, changes to the quest log, various tweaks, a good number of balance changes, and so much more.
I actually think there isn't one thing that hasn't had some sort of adjustment in this patch. The 6.0.2 Iron Tide patch should be rolling out soon if it's not out already by the time you read this.
(h/t PC Gamer)
