FOLIO, 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 so folded is a book of the largest size and is known as a "folio" (see BIBLIO GRAPHY). 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 writ ten ; in law-writing, for a fixed number of words in a legal docu ment, used for measurement of the length and for the addition of costs. In Great Britain a "folio" is taken to contain 72 words, ex cept in parliamentary and chancery documents, when the number is 9o. In the United States ion words form a "folio."