Should there be a tag for Gaussian elimination?
It’s a reasonably common question topic, presumably since it’s a standard part of the math curriculum at many universities (and also lends itself particularly well to homework problems). Searching for it shows over 500 existing questions — more questions than about 6/7 of existing tags have.
The previous meta question New tags: when? unfortunately doesn’t give much guidance, apart from “if not sure, ask Meta”.
(Prompt for asking: I just asked a new question about Gaussian elimination/Smith normal form, and couldn’t find any tags better than the very wide-ranging matrices and linear-algebra.)