The immediate-reaction tag currently has no tag info, but there are seven D&D 4e questions with the tag.
reactions is currently used on 92 questions, all but one of which are apparently for D&D 5e. (The only other one is about Mutants & Masterminds. I recently found another M&M question it might apply to, which is what made me discover this issue.)
The tag info for the reactions tag says:
For questions about reactions - an action taken by an entity in response to a trigger happening.
Do these two tags describe essentially the same type of thing? If so, should they be synonymized?