This excerpt taken from the AMZN 10-K filed Feb 17, 2006.
Amazon Enterprise Solutions (formerly known as Merchant.com) provides third party retailers with back-end e-commerce and fulfillment solutions to enable third party e-commerce businesses operating under their own brand name and website address (e.g. www.target.com). We also offer web services applications to developers. In addition, we have co-branded credit card agreements and marketing and promotional services, such as online advertising.