is it acceptable to put questions of the type "what does ... mean?" or "what is ...?" on MathOverflow. For example?

  • what is the moduli space of higgs bundles?
  • what is a Picard-Viessot extension?
  • what is a Borel subgroup?
  • what is the Kontsevich-Zorich cocycle?
  • ...
  • etc

There are many examples of literature where the jargon is so specific I have no idea what they are talking about. Perhaps it's time to contact the author?

  • 2
    $\begingroup$ Terminology is either standard or it is defined before it is used. -- In the former case you can just google for the definition, and in the latter case you need to look up the definition in the book or paper where it is used. I think in none of these cases asking for a definition is on-topic on MO. $\endgroup$
    – Stefan Kohl Mod
    Commented Dec 16, 2016 at 18:34
  • $\begingroup$ I think that (allowed-questions) would be a suitable tag here. (Not enough rep to edit on meta, so posting a comment instead.) $\endgroup$ Commented Dec 17, 2016 at 6:25
  • $\begingroup$ Although the standards of this site (and of other sites in SE network) change over time, it might be reasonable to check similar questions from the past. Also, if I see the title:"What is A?", it is possible to interpret it as: 1) I know the definition of A, but could you help me get some insight into what this actually means. 2) The notion A is used in this paper without a definition. Can someone with knowledge of that field give the definition and some references? You are talking about the possibility 2), right? $\endgroup$ Commented Dec 17, 2016 at 6:30

1 Answer 1


Some of the questions are okay, and some are not. It really helps if you ask the question in a way that indicates that you've done your homework.

For example, if you just want a definition of Borel subgroup or some basic context, you might as well read the Wikipedia article, or even better, consult a standard text on algebraic groups. The same is more or less true for Picard-Vessiot extension. If you want something above and beyond such references, then your question should not have the simple "what is" form, and should be more specific.

One situation where such a question is (in my view) unambiguously reasonable is if you are asking about something that has appeared recently. In this case, there may not be standard references, and it is possible that only a few specialists have a good grasp of the mathematical context. In this case, you shouldn't be surprised if it takes a while for a good answer to appear.


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