When we say folio we mean page number — usually anyway.

To begin with, however, the word referred to a page number which only appears on the front of the sheet; you’d have folio 23 recto and folio 23 verso. In this system which went out of fashion relatively early in the history of the printed book, what we think of as a 256 page book would end with folio 128 verso.

As John Carter tells us in ABC for Book Collectors, the word then moved on to refer to “the numeral itself in a foliated book or MS., and thus by a confusing extension the printer’s name for page numbers of any sort. Normally included in the headline, they might also appear at the foot, along with the catchword.”

The word also can refer more expansively to a book of folio format, consisting of sheets which have been folded only once. By extension it can also refer to “a large book”.

Imposition of a folio sheet, outer side above, inner below. The watermark and countermark make things clear.











A folio could also be a portfolio, the carrier in which you might transport that folio book or your large papers. This of course generalizes out to a portfolio of investments, or your area of responsibility as a government minister.

The word folio comes from the ablative of the Latin, folium, a leaf, from which of course, foliage, and via France, foil, as in gold foil. (The light sword thus named seems to have a different etymology, though the OED confesses it doesn’t know what it is.) As a verb foil also has an interesting and varied life, including quaintly “to subject land to the third of a series of ploughings”.