Stack Exchange network consists of 178 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.
Q&A for work
Connect and share knowledge within a single location that is structured and easy to search.
The undo looks useless and I think it needs removing.
Currently it is only used on one question (which is a duplicate of another question which didn't use the tag and got answers).
I can't see undo being used anywhere else.
It was just created, new users create these all the time however we don't normally have tags for simple features like this, it has been removed.