I understand what an accepted answer is, and also what an unanswered question is. However, I don't know the difference between "advice" about an answer, what is an "appropriate" answer, or a "howto" for answers. I don't even see how they're much more use than just posts about answers. Shall we burninate "answering-advice", "appropriate-answers" and "answer-howto"?
Does it describe the contents of the questions to which it is applied? and is it unambiguous?
No, I can't tell them apart.
Is the concept described even on-topic for the site?
It's on-topic for meta, yes.
Does the tag add any meaningful information to the post?
A very small amount.
Does it mean the same thing in all common contexts?