Bookbinders use the word folio at times. There are several meanings for this ~ and confusion might arise if either speaker or listener has different views on the matter. There is no need to plough through all of this page ~ just explain in longhand what you are talking about ~ or ask for a clearer definition of what you are hearing.
A prime example of confusion is caused by the familiar use of the ISO-A sizes. Strictly an A4 folio results in an A5 finished product. Buut I doubt if most customers would understand that. Besides landscape books are now popular and you cannot make an A5 Landscape book from an A4 sheet. So the ~ old fashioned ~ definition of folio is the size of the starting page ~ might be misunderstood.
The solution to any problem is to avoid the use of the word folio ~ it is rarely necessary ~ and also ~ use common, clear, unambiguous language, such as 'It will finish at size A5 with a landscape format.'
Apologies for going on about confusion, but at several times during my printing career knowledeabe people have asked for a book 'to be printed in A4 portrait format'. They have the knowledge that to make a book I would start with an A4 sheet. Correct. If it is to finish in A4 portrait I would need to start with A3 sheets. If I start printing on A4 I could print four-pages-up and finish with an A5 portrait book. Has this paragraph confused you? Good. You do have to sort it out in both your minds when discussing things. Fortunately I never did print and bind 50x100pp books all of the wrong size. There is a lot at stake! (And - to stir things up more sometimes perfect binding was ~ is ~ acceptable. It involves yet more different printing techniques, since folios are no longer necessary. And finally ~ not all litho and digital printers use A4 printing machines.
Folio has a number of meanings. Throughout this site I concentrate on just one meaning ~ a single sheet of paper that has been folded ~ just once ~ to form a mini book ~ of four pages ~ two leaves ~ one sheet [115136].
There are other meanings ~ mentioned below. Hence the need for me to avoid confusion by describing the paragraph above. My 'folded sheet' descriptor, above, does not have any other simple, one word, to explain it. That is why I am clarifiying my use of it throughout the rest of this site.
The folio is the main element to the whole history of codex-style bookbinding [125223].
Other meanings attached to the word folio are normally clear from the context, but they can also lead to misunderstandings ~ always something to be avoided.
A folio is understood by some people to mean a single sheet of paper, or a leaf. For some the leaf has to be numbered in order to quaify as a folio.
A folio is sometimes interpreted as a large book. (As in Shakespeare's plays. A quote from a past Christie's Auction Catalogue lists the following item ~ 'The First Folio # 1623 ~ contains 36 plays, 18 of which had not previously been printed, and which would otherwise have been lost forever.' Their estimate of the value of a similar book was £1million.)
Sometimes a folio might refer to one half of a sheet once it has been cut into two pieces.
The word portfolio is sometimes shortened to folio, because of the folded V-shape of the covers.
I believe a folio can also mean a bundle of accounts or a particular legal document ~ the characteristic being that just one number refers to the whole thing ~ which maybe has four pages ~ or not. (As, maybe, 'see folio 23ff'.) I am not prepared to get entangled with either the accountancy or legal professions, but would as always, be glad to share any knowledgeable and reliable information.<'/p>
Similar entanglements ensue when talking about old documents. Typically the folio itself is numbered ~ rather than the two sides it sometimes has ~ or maybe the four ~ sides. The number is then appended with recto or verso to describe which of the 'pages' are being discussed [112703]. Theis causes abbreviations such as 'f3 r.' and 'f27 v.' It is good typestting practice to restrict the length of line to ~ about ~ ten words. On a large sheet this requires the use of columns ~ eg newspapers. These are lettered a~b~c. This we arrive at 'f3 v. col. b'. I am entangled enough.