Selling partner: A selling partner can be a seller or a vendor.
Seller: A seller lists and sells their own goods on Amazon's retail website. After an item is sold, it is either (1) directly fulfilled by the seller using inventory managed by the seller, or (2) fulfilled through the Fulfillment by Amazon (FBA) program, using the seller's FBA inventory.
Vendor: A vendor supplies the inventory that is sold by Amazon on Amazon's retail website. There are two main types of vendors: Retail procurement vendors and Direct fulfillment vendors.
Retail procurement vendor: A retail procurement vendor sells inventory to Amazon and ships it to Amazon's fulfillment centers. Amazon then sells and ships the inventory to customers who make purchases on Amazon's retail website. A retail procurement vendor can be a brand owner or a distributor. In some cases they manage the listings of the products that they supply to Amazon.
Direct fulfillment vendor: A direct fulfillment vendor ships orders to customers on Amazon's behalf. After a customer makes a purchase from Amazon on Amazon's retail website, the direct fulfillment vendor ships the order directly to the customer.
Public application: An application that is publicly available and is authorized by a selling partner.
Private application: An application that is available only to your organization and is self-authorized.
Public developer: A developer that builds and offers publicly available applications that are used by other companies.
Private developer: A developer that builds application(s) that integrate their own company with Amazon APIs.