What is a “canonical answer”?

Question

I'm confused. There appears to be conflicting ideas as to what constitutes a canonical answer on EL&U.

Simply saying it is the best answer, is too subjective. Best for whom? Best for the OP who is asking the question? But how would the user recognize the best answer without some previous knowledge? Best because of the number of upvotes an answer receives? But sometimes the funniest and cleverest answers are the most upvoted ones, and therefore, objectively speaking, not necessarily the most correct. Best because the answer is beautifully written in flawless English?

Please see the most recent bounty set up for: A word for a "non-logged in" user
I am confused as to why the user offering the bounty believes his answer (currently standing at 70 upvotes) is not ‘canonical’. There is, however, an answer that has 80 upvotes so far, an eighteen-word-long post. Would anyone agree a single sentence answer is canonical because it has more upvotes than any other?

Here are three more examples of bounties set up with the aim of receiving a canonical answer.

1. Framing a question whose answer is an ordinal number
   This post earned the bounty because it had the largest consensus.
2. How can I reliably and accurately identify the passive voice in writing or speech?
   Here the bounty was NOT awarded to the highest upvoted answer.
3. Did English ever have a formal version of "you"?
   Objectively speaking, the user awarded the bounty is EL&U's most authoritative user/author. Does that mean the answers which earned 415, 78, 41, and 31 upvotes are not canonical?

If we take for granted an answer consisting of one or two sentences can rarely be considered canonical; that EL&U encourages every user to support their answers with references and cited sources, and a wrong answer cannot be ‘canonical’, what exactly is a canonical answer?

Can someone please explain what the criteria is?

1. Is it based on the number of upvotes an answer receives?
2. Is it the most “accurate” and/or most “correct” answer, regardless of the number of upvotes?
3. Is a canonical answer the most objective?
4. Is it the most authoritative because of its author?
5. Is it the best written? (due to style and accuracy)
6. Or something else?

Can users please provide examples of canonical answers that they believe are exemplar and explain why?

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If we can agree what makes a canonical answer, would it not be best to mark it some way so that users and visitors can easily identify it? That way we block users from setting up “canonical” bounties on questions which have been abundantly and satisfactorily answered.

This feature would not prevent bounties on questions and answers that need to be updated (although an answer replying to a grammar question five years ago is still going to be a correct answer today) or awarding bounties on answers that are considered worthy of greater attention.

Answer 1

Of course there is no clear definition for 'canonical', any more than for 'best' (which is presumably why Stack Exchange per se uses neither term). There is, however, general agreement that some answers are better than others; each voter decides which post or posts to upvote, and the highest-voted is the best in the 'opinion' of ELU as a whole, no matter what you or I may think of it (the accepted answer is presumably the best in the opinion of OP).

Similarly, there is general agreement that certain questions are asked repeatedly, and it would be useful to (for example) close every "What is the question to which the answer is Xth?" question as a duplicate of one particular example. There is, however, no agreement, far less an official line, on which example that should be. So you close the next one as a duplicate of your preferred example, I will do the same with mine, and perhaps a canonical post will emerge.