A site is a group of related Web pages where your team can work on projects, conduct meetings, and share information. Your organization can use subsites and top-level sites to divide site content into distinct, separately manageable sites. For example, your organization may want separate sites for each product or region.
Top-level Web sites can have one subsite or multiple subsites, and subsites in turn can have multiple subsites. The entire structure of a top-level Web site and all of its subsites is called a site collection.