Another tag I’ve come across with no description is estimations. I think it’s trying to cover questions involving giving or otherwise dealing with estimates, but I find the plural a bit confusing if I interpret estimation as “act or instance of estimating”.
There’s only 6 questions tagged with it, but I didn’t see a better existing tag, so I’m not sure I’d want it disappeared entirely. However, since it’s used on so few questions it probably wouldn’t be a big loss if others felt it wasn’t useful.