Site definitions are the collection of XML or ASPX files and can contain all the necessary components. They are packaged in SharePoint solution files (.wsp) and are easy to transport since everything you need is packaged into a single file. Site definition contains information of web parts, lists, libraries, features, and navigation bars to be included in the site.
Site definition contains three files:
â€¢ webTemp.xml: Created for every language version and contains the entries for the template selection box on the site creation page.
â€¢ onet.xml: Contains one or more configurations for a site template, including specification of all components used, such as features, lists, and Web Parts
â€¢ default.aspx: Empty page