I looked around on meta but can't seem to find a question about this, so here goes.
Posting this question this evening, I looked for a shape-operator tag. This tag wasn't present, but I saw shape, which currently has no guidance or tag wiki. I tried to look at the questions to figure out what it was for, but I don't seem to find a pattern. Mostly it seems to be used for "simple" questions about… well, "shapes".
What can we write as a tag wiki?