1. A leaf. In the ancient law-books it was the custom to number the leaves, instead of the pages; hence a folio would in-dude both sides of the leaf, or two pages. The references to these books are made by the number of the folio, the letters “a” and “b” being added to show which of the two pages is intended; thus “Bracton, fol. 100a.”
Source: Black’s Law Dictionary 2nd Ed (1910)
