An online marketplace refers to a type of Ecommerce store where various merchants can sell their goods to potential customers. A current example of quality online marketplace includes Shopify, Amazon, eBay, and Etsy. Even Airbnb follows the same business model. The key is to be the bridge between businesses and customers rather than selling products and services yourself.
This is starkly different from the traditional Ecommerce model. Instead, the merchants that sell products through your platform will be using the conventional model. For instance, Shopify as a whole caters to various merchants and hence will be referred to as an online marketplace. On the other hand, a single brand operating in Shopify will be referred to as an online store.