The Second Life Marketplace, often just called The Marketplace, is a web-based store operated by Second Life where Residents can purchase products to use In-world.
The Marketplace is a convenient place to shop for items from among thousands of creators, however, because it charges them a small fee for every item sold, many creators offer the same items in their in-world stores for lower prices, or keep older items in their Marketplace stores so they can keep their in-world locations just for their newer creations.
The website for the Marketplace is https://marketplace.secondlife.com/.