Walmart, of course, is the largest retailer in the world with nearly $500 billion of worldwide sales.
The company liquidates excess inventory in several different ways. They have a long history with Jacobs Trading, now owned by Liquidity Services (which operates Liquidation.com). They have also had contracts with a small number of other liquidators over the years.
In addition, for the past 4 or 5 years, they have operated their own liquidation marketplace to allow any company with a resale certificate and a US shipping address to buy from them directly. The marketplace is located at http://liquidations.walmart.com and it is operated by B-Stock Solutions.
The site is an auction based format and listings range from single pallet to full truckloads. The inventory comes from 6 different distribution centers but there tends to be a heavy dose of product from Waco, TX. The inventory itself tends to be mixed categories, including: TV's, Furniture, Outdoor, Home Improvement, and many others.