Fol·io n.; pl. Folios
 1. A leaf of a book or manuscript.
 2. A sheet of paper once folded.
 3. A book made of sheets of paper each folded once (four pages to the sheet); hence, a book of the largest kind. See Note under Paper.
 4. Print. The page number. The even folios are on the left-hand pages and the odd folios on the right-hand.
 5. A page of a book; Bookkeeping a page in an account book; sometimes, two opposite pages bearing the same serial number.
 6. Law A leaf containing a certain number of words, hence, a certain number of words in a writing, as in England, in law proceedings 72, and in chancery, 90; in New York, 100 words.
 Folio post, a flat writing paper, usually  17 by 24 inches.