A tag had lost magically according to Post History
In the above picture according to history it says that Mark Giraffe had added definition tag. Then, Mithical had added support tag (But, somehow two definition tag had arisen in left diff). Later, definition tag had gone magically.
What I think that is, Mithical had added support tag to migrate that question to Meta category. Later, she had removed definition tag maybe.
But, post history doesn't explain where definition tag had gone.
When I have visited that history page again, I had seen that now, the support tag have became secrets (in history only). Even, in Initial Revision that tag have become secrets. (Is magic happening?)
More weird thing, when I click on secrets tag it directs me to this page (Note : Category ID is Meta). Although, it shows Q&A question. Even, there's no secret tags in Meta.