Copied from http://www.mmo-champion.com/

So ... What does it mean? Well, Wrath of the Lich King was trademarked a few weeks before the Blizzcon, we're not going to jump to conclusions here but WoWWiki will most likely give you a few things to think about on their Great Sundering article.

The Great Sundering, also known as simply the Sundering or the Cataclysm was a world event which reshaped Azeroth approximately 10,000 years ago at the end of the War of the Ancients. This event was triggered due to the Well of Eternity being destroyed.

Prior to the Sundering, there was only one continent on Azeroth, referred to as Kalimdor. In the catastrophic explosion, eighty percent of the land mass was destroyed leaving behind the major continents and scattered islands that are known today: Northrend, Kezan, the Eastern Kingdoms, and the remnant still referred to as Kalimdor.

The site of the Well of Eternity became a swirling vortex of power known as the Maelstrom.