A tag synonym makes two or more tags behave as one tag when tagging a question. It's most often used when a different term can mean the same thing (e.g. [united-nations] and [un]). Use this tag to discuss creating or removing synonyms.
Tag synonyms can also be proposed by those with at least score 5 in the main tag. For example, to propose a synonym for united-states go to
https://politics.stackexchange.com/tags/united-states/synonyms. This link is also available from the tag itself.