"Marketplace" refers to 3rd parties selling on the platform. Until recently, Walmart.com was exclusively products sold by Walmart - now they let 3rd parties list and sell products too (just like Amazon).

Are you familiar with a planogram? Walmart the physical location is a platform, with paid placement for premium locations on a shelf. Same goes for virtually all national retailers.

Hell, Frito even has their own employees stock the shelves, which is why the chip aisle tends to look immaculate compared to the rest of the store.

Third parties have been selling at physical Walmart stores beside store brands for decades. The same with every drug chain.

So if Walmart.com has a million products that are drop-shipped from whoever, those would be/could be still considered "sold by Walmart"? Or are you saying this is equivalent to Amazon, but only started yesterday

Something sounds odd, because I interviewed with a no-name company that handles this sort of thing close to a decade ago, and while I don't remember if they did it for Walmart, they provided similar fulfillment services for several large e-commerce websites.