The tag is present in Lintian version 2.104.244. That is the most recent version we know about.
The listed packages from the same source circularly depend (or pre-depend) on each other. This makes it difficult for tools to properly handle install/upgrade sequences. Furthermore this complicates automated removal of unused packages.
If possible, consider removing or reducing one of the depends.
Note: This check is limited to packages created from the same source package. Full circular dependencies between binaries from different source packages is beyond the scope of Lintian.
Refer to Debian Policy Manual section 7.2 for details.