FORMAT is the shape and size of a book. In bibliographical contexts, it is used to indicate the size of a volume in terms of the number of times the original printed sheet has been folded to form its constituent leaves. Thus, in a folio each sheet has been folded once, in a quarto twice, in an octavo three times; the size being respectively a half, a quarter, and an eighth of the original sheet.
A FOLIO is 1) a leaf numbered on the recto, or front; 2) the numeral itself in a foliated book or manuscript; 3)A book of folio size, whose quires consist of full sheets of papers folded once, and double the size of the ordinary octavo.
A QUARTO is a book essentially squarish in shape and normally lying between folio and octavo in size. A full sheet of paper is folded twice.
An OCTAVO is the most common size of book since the 17th century, based on a sheet folded three times
RECTO is the front, or obverse, side of the leaf; i.e.the right hand page of an open book or manuscript.
VERSO is the back, or reverse, side of the leaf; i.e. the left-hand page of an open book or manuscript.
A CATCHWORD is the first word of the following page inserted at the right-hand lower corner of each page of a book, below the last line.
SIGNATURES are the letters (or in some modern books, numerals) printed in the tail margin of the first leaf (at least) of each gathering or section of a book, as a guide to the binder in assembling them correctly. Signatures normally run from A to Z, omitting by convention, J and U, which in earlier days were capitalised as I and V, and also W. If the whole alphabet has been run through, they usually proceed to AA, BB, or Aa, Bb, etc.
A GATHERING (or QUIRE) is the group of leaves formed after the printed sheet has been folded to the size of the book and before it is combined in the proper order with its fellows for binding. The SHEET is the printer's unit, the LEAF the bibliographer's. The GATHERING is the binder's unit. In octavos, the gathering usually comprises one sheet folded three times.
FOLIATION is the numbering of leaves, as opposed to pagination which is the numbering of pages. It is rare in books printed before 1475, when the majority bore no consecutive numeration at all; or after 1600, by which time it had generally given place to pagination.
PAGINATION is the sequence of figures with which the pages of a book are numbered. These are known individually as page-numerals, collectively as pagination.
DECKLE EDGES are the rough, untrimmed edges of a sheet of hand-made paper (the deckle being the frame or band which condines it in manufacture)
INTAGLIO is the engraving processes in which the image is incised into the plate, as opposed to those where the surfaceis cut away leaving the image in relief.
FOUNT or FONT (OF TYPE) is the style and size of the type. in the strict sense, a printer would order from the typefounder a "fount (i.e. a complete set) of pica (= 12-point) Caslon".