A native source package is one that does not distinguish between Debian packaging releases and upstream releases. A native source package contains a single tar file of source material, and the versioning does not have a Debian-specific component. Native packages are normally (but not exclusively) used for software that has no independent existence outside of Debian, such as software written specifically to be a Debian package.
Source packages should specify the most recent version number of this policy document with which your package complied when it was last updated.
The version is specified in the Standards-Version control field. The format of the Standards-Version field is described in Standards-Version.