"Insurance Exchange"? WTF?

Someone explain what an "Insurance Exchange" is, seeing as how Obama will apparently tout it this evening...

Now, if you’re one of the tens of millions of Americans who don’t currently have health insurance, the second part of this plan will finally offer you quality, affordable choices. If you lose your job or change your job, you will be able to get coverage. If you strike out on your own and start a small business, you will be able to get coverage. We will do this by creating a new insurance exchange – a marketplace where individuals and small businesses will be able to shop for health insurance at competitive prices. Insurance companies will have an incentive to participate in this exchange because it lets them compete for millions of new customers. As one big group, these customers will have greater leverage to bargain with the insurance companies for better prices and quality coverage. This is how large companies and government employees get affordable insurance. It’s how everyone in this Congress gets affordable insurance. And it’s time to give every American the same opportunity that we’ve given ourselves.