The tag is present in Lintian version 2.104.234. That is the most recent version we know about.
This package declares a Breaks relationship with another package that has no version number. Normally, Breaks should be used to indicate an incompatibility with a specific version of another package, or with all versions predating a fix. If the two packages can never be installed at the same time, Conflicts should normally be used instead.
Note this tag can also be issued if a package has been split into two completely new ones. In this case, this package is missing a Replaces on the old package.