I have read it a lot under many questions in EL&U and even ELL. It is one of most ambiguous terms which I have read here. Please discuss about it to make it clear for all users as well for mods to not misuse it under any questions. Is there anything about in FAQ to explain it definitely?
Throughout the SE system a constructive question is one which demands clear, unambiguous, evidentially supportable answers as opposed to varying and mostly personal opinions. Here is what the FAQ says:
As it currently stands, this question is not a good fit for our Q&A format. We expect answers to be supported by facts, references, or specific expertise, but this question will likely solicit debate, arguments, polling, or extended discussion.
For instance, “Which is better, American spelling or British spelling?” is Not Constructive—if people could agree the question would never even arise. But “Will this sentence in American spelling be misunderstood by British readers?” is Constructive—if any misunderstanding is in fact possible, posters will tell you exactly where the misunderstanding arises, and will probably also suggest workarounds to avoid misunderstanding.
1) If a question doesn't seem like a good fit for this site, people can vote to close. When they do, they are shown a screen that looks like this:
We can pick apart the meanings of "not constructive" and "too localized" all we want, but, in the end, they both simply mean: "out of all the reasons I could have voted to close this question, this is the reason that seems to fit best."
2) When a question is closed, that simply means no more answers will be accepted. You don't lose rep points for having a question closed. The answers don't go away. People can still read the question, and leave comments. The question can still be upvoted and downvoted. It's not a punishment, it's a mechanism to help visitors and regular members direct their valuable time and energies toward better questions. Remember, answers take time to compose, and most regulars on the Stack Exchange have a very finite amount of free time.
3) When a question is closed, it can be improved, and it can be reopened. In fact, some closed questions do get reopened. Sometimes a question gets judged too quickly, when those who voted to closed failed to see some deeper nuances. However, more often than not questions get reopened after they have been improved.
4) Most closed questions fail to provide enough context. If my question was closed, I would invest my energy into improving it, rather than arguing with people about it. (I certainly wouldn't make wholesale insults to the community at large; that's not likely to garner much support.)
5) I've seen very few closed questions that couldn't stand a little improvement: tell us where you found the phrase, show us what research you already did, explain a little more about why you are confused. Make it less vague and more pertinent. Ask for help, and listen to the advice you're given.
6) I don't necessarily agree with all close votes, and I've even actively campaigned to get some questions reopened. But I also understand this is a community, that we all have our own opinions – and I respect that. That's why it takes five votes to close a question, and that's why five more votes can override those votes, and reopen the question.
7) Yes, moderators can close questions unilaterally, but don't complain about that. Moderators are respected, trusted members of the community, and they have a right to exercise their best judgment. It's also worth noting that even a moderator's closure can be overridden by five members of the community, so, please, no railing about perceived injustices.