Site definition are deployed within 12\template\sitetemplates directory and
are referenced in 12\template\1033
A site definition itself does not represent a creatable site template. Instead, a site definition contains one or more configurations, and these configurations are what appear to users as creatable site templates.
Site definition --contains--> configurations <--referenced by webtemp*.xml --> display configuration as creatable site template
When creating a new site by using the STSADM.EXE command-line utility or through custom code, you are often required to reference a site definition and one of its configurations by name. This is done by specifying the name of the site definition followed by the pound sign and the integer identifier of the configuration. For example, you can use STS#0 to reference the site template titled Team Site and STS#1 to reference the site template titled Blank Site. The following example uses one of these site template references when creating a new top-level site by using the STS command-line utility.STSADM.EXE -o createsite -url http://site.com -ownerlogin xx\xx -owneremail firstname.lastname@example.org -sitetemplate STS#1