a sheet of paper folded once to make two leaves, or four pages, of a book or manuscript.

a volume having pages of the largest size, formerly made from such a sheet.

a leaf of a manuscript or book numbered only on the front side.

Printing .

(in a book) the number of each page.

(in a newspaper) the number of each page together with the date and the name of the newspaper.

Bookkeeping . a page of an account book or a left-hand page and a right-hand page facing each other and having the same serial number.

Law . a certain number of words, in the U.S. generally 100, taken as a unit for computing the length of a document.

pertaining to or having the format of a folio

a folio volume.

to number each leaf or page of.

Law . to mark each folio in (a pleading or the like) with the proper number.