the system of numbering pages
"After the binding shop renumbered every page, we had to update our entire folio to match the new sequence."
a book (or manuscript) consisting of large sheets of paper folded in the middle to make two leaves or four pages
"the first folio of Shakespeare's plays"
a leaf of a book or manuscript
"The rare manuscript was so fragile that conservators had to handle each folio individually with padded tongs."
to put a serial number on each folio or page of (a book); to page
"The archivist carefully numbered every folio in the ancient manuscript to ensure no pages were misplaced."