FOLIO (properly the ablative case of the Lat. folium, leaf, but also frequently an adaptation of the Ital. foglio), a term in bibliography and printing, with reference either to the size of paper employed, or of the book, or to the pagination. In the phrase "in folio" it means a sheet of paper folded once, and thus a book bound up in sheets thus folded is a book of the largest size and is known as a "folio" (see Bibliography). Similarly, "folio" is one of the sizes of paper adapted to be thus folded (see Paper). In book-keeping the word is used for a page in a ledger on which the credit and debtor account is written; in law-writing, for a fixed number of words in a legal document, used for measurement of the length and for the addition of costs. In Great Britain, a "folio" is taken to contain 72 words, except in parliamentary and chancery documents, when the number is 90. In the U.S.A. 100 words form a "folio."
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)