For questions about whether two tags should be separate or merged together.

The tagging system on Stack Exchange supports tag synonyms; basically, this is a redirect between tags, so that an attempt to use one tag causes it to be treated as the other tag. This mechanism is useful when two tags have interchangeable meanings.

On PPCG Meta, the tag is used for questions about whether synonyms should be created/deleted/modified; in other words, it's for questions about whether two tags are the same, or different.