What exactly is an "unpublished paper"? In applying to the NSF postdoctoral fellowship for mathematics, the instructions include the following paragraph for the biographical sketch:


  A list of: (i) up to five products most closely related to the proposed project; and (ii) up to five other significant
  products, whether or not related to the proposed project. Acceptable products must be citable and accessible
  including but not limited to publications, data sets, software, patents, and copyrights. Unacceptable products are
  unpublished documents not yet submitted for publication, invited lectures, and additional lists of products. Only
  the list of 10 will be used in the review of the proposal.


My question is what exactly does "unpublished" mean? Is a paper uploaded to the arXiv but not yet submitted for publication in a journal considered "unpublished"?
I would interpret "published" to mean exactly what the text says — citable and accessible.

ArXiv papers are both citable and accessible, and therefore do count as acceptable research products.