a sheet of paper folded once, or the size of each of the two leaves so formed
a book printed on pages of this size
a book of the largest size
(used before a noun) consisting of folio-size pages
a folio edition
a leaf of a manuscript or book
a page or leaf number
a case or folder for loose papers
a certain number of words taken as a unit in measuring the length of a document
[Middle English from Latin, ablative of folium]