The tag is present in Lintian version 2.104.234. That is the most recent version we know about.
This udeb package appears to be empty, and its description does not say that it's a metapackage or a package. This is often due to problems with updating debhelper *.install files during package renames or similar problems where installation rules don't put files in the correct place.
If the package is deliberately empty, you can avoid this tag by using one of the following phrases "metapackage", "dummy", "dependency package", or "empty package" in the long description of the udeb.
This tag is experimental.