Taking a quick look at the posts tagged "overlay" then I can see two obvious distinct meanings:
- Beamer's overlay mechanism
- Overlaying some text on top of other text, usually one symbol on top of another.
My feeling is that these are truly distinct and should therefore be separated. Since "overlay" is always going to be ambiguous, we should have proper forms that are not ambiguous and then make "overlay" a synonym for the most used (or perhaps the most used by new(ish) users, if that's possible to work out ... where's Paulo's expertise with the data explorer when you need it?).
So ... how about: beamer-overlays and symbol-overlays (not sure what our style is on plural/singular for the main tag). We could also have the more generic text-overlay (though I doubt that would come up so much).