A site definition is one defines a site. When we install sharepoint or wss then we get out of the box site definitions like team site, blank site, meeting work space etc. To be clear when we create a site from team site it has task list, one document library etc., i.e a site definition defines what a site includes.
Before understanding more of the site definitions we will go through the inner workings of the sharepoint.
To be continued .... .....
