Amazon Marketplace is an e-commerce platform owned and operated by Amazon that enables third-party sellers to sell new or used products directly to consumers on a fixed-price online marketplace alongside Amazon's regular offerings. Using Amazon Marketplace, third-party sellers gain access to Amazon's customer base, and Amazon expands the offerings on its site without having to invest in additional inventory.
This is in contrast to first-party sellers (1P sellers) who act as wholesale suppliers that sell goods directly to Amazon. Amazon calls these sellers "vendors" and they operate using Amazon's Vendor Central.