Websites, Stores, and Views

Every Magento installation has a hierarchy of website(s), store(s), and store view(s). The term scope determines where in the hierarchy a database entity — such as a product, attribute, or category — content element, or configuration setting applies. Websites, stores, and store views have one-to-many parent/child relationships. A single installation can have multiple websites, and each website can have multiple stores and store views.

Magento installations begin with a single website which by default, is called Main Website. You can also set up multiple websites for a single installation, each with its own IP address and domain.
A single website can have multiple stores, each with its own main menu. The stores share the same product catalog, but can have a different selection of products and design. All stores under the same website share the same Admin and checkout.
Store Views
Each store that is available to customers is presented according to a specific view. Initially, a store has a single default view. Additional store views can be added to support different languages, or for other purposes. Customers can use the language chooser in the header to change the store view.

To learn more, see Multiple websites or stores in the Magento developer documentation.