Folio

A folio (from the Latin folium or leaf, pl. folia) is a sheet of paper, or the two sides of the sheet of paper. It is not to be confused with a page, which is just one side of a folio. Early systems of pagination number the folio, not the page, with the initials 'r' (for recto or right-side or front) and 'v' (for verso or opposite or back or reverse). Thus page 1 is 1r, page 2 is 1v, page 3 is 2r, and so on.

A bifolium is a sheet folded in two to make two folios, one on each side of the fold. A stack of bifiolia sewn together is a quire.

If there are four bifolia (making eight folios, or sixteen sides) then the quire is a quaternion, the most standard size of gathering (although most manuscripts include quires of varying sizes, so 'standard' does not imply uniformity). [1]