This is the type of book we'll be concerned with here. The definition of "Book" is chimaerical at best, but for the sake of brevity we'll limit this explanation to fairly modern Western binding styles and leave clay tablets, scrolls, and accordions for another time. 
Binding can refer to the binding style of a book (i.e. hardcover) or to the act of assembling a book from its individual pages. Western books were traditionally sewn, signature by signature, on linen cords or tapes, but this process has more recently been replaced by hot glue bindings
which hold the spine ends of the pages together, sometimes with sewing as a re-enforcement.Two binding styles often stated in dealer's catalogs are half bound (on the left) and quarter bound (on the right). Half bound means that the book has leather or other binding material on the spine and at the fore-edge corners. A book bound in this style, but with a greater area covered by leather than the normal half bound book, is sometimes called three-quarter bound. Quarter bound means that there are no pieces at the fore-edge corners. This can be remembered by the percentage of the boards covered with the structural binding material. The book at the left has approximately 50% of the board covered while the book at the right has approximately 25% of the board covered. The remainder of the board is often covered in marbled paper (as the one on the left is) or decorative paper (as the one on the right is), though sometimes another leather or cloth is used in place of this paper. These terms often are abbreviated and used as a prefix in descriptions, so a book that is half bound in calf would be stated by a dealer as "half calf".
- Folio (Fo. ): One sheet of paper folded. In the illustration above the folio arrived at would be 24"x 36", larger than average. A folio is loosely analogous to coffee table book size, as long as the fore-edge and spine are longer than the head & tail . Folio, definition two, is any folded sheet of paper. As an example one would probably have three or four folios in a signature. Each folio would have two leaves . And each leaf would have two pages, one on each side.
- Quarto (Qto, 4to.): This is, after cutting, one half of a sheet of paper folded. Basically it is one Folio ripped in half and made into two folios.
- Octavo (Oct., 8vo): If you've noticed as trend here then you are catching on. The parenthetical abbreviation indicates how many leaves are produced from the folding of the paper, in this case 8 leaves or 4 folios.
- Duodecimo (12mo, sometimes pronounced "twelvemo") Duodecimo (and the following) follows the same trend as the above and becomes more difficult to describe even in a thousand-word format.
- Sextodecimo (16mo, pronounced "sixteenmo" by the lazy)
- Vicesimo-Quarto (24mo, pronounced "twentyfourmo" by the less than bold)
- Tricesimo-Segundo (32mo, pronounced "thirtytwomo" by nearly everyone)
- As New is a fairly obvious one. This describes a book which could have just come from the binder. It must be free from defect both in binding and dustjacket (DJ). This term is preferred to the sometimes used mint.
- Fine (F) describes a book which falls just short of As New. It lacks the crispness of a the above, but is otherwise free from defect.
- Very Good (VG) copies show some signs that they've been handled and probably read ("eye-tracks" do indeed decrease the value of a book, but please don't stop reading). This is basically a used book which was previously owned by a little old lady who only took it out on Sundays to drive to church.
- A Good (G) book is one which is definitely used and worn but is still solid and all pages are accounted for.
- Fair copies still have all of their text pages and illustrations but could be missing other things like endpages or fly-leaves. Fair books are even more definitely used than Good books, but a Fair book is still up for a few years of faithful service.
- Poor (P) describes a book which is nearly the polar opposite of As New. A Poor book should have the complete text, but anything else is up in the air. This is a book which tom-catted around and generally led an unhealthy life, but may still have value as a Reading Copy.
- A few other terms to note:
- Ex-Library is another term whose definition is fairly straight-forward. This describes any book which belonged to a library. Ex-Library copies may have been rebound, had things pasted in, have glued down flaps on the dustjacket, and all of the rest of the things which happen to books in libraries. An Ex-Library copy must always be noted as such in any description of the book.
- A Book Club Edition is an edition manufactured specifically for a book club. They are usually printed and bound poorly to cut down on overhead and do not carry the value of an edition produced for the trade. Some book clubs reprint the trade edition's copyright page exactly, so there is sometimes confusion about whether a copy is a Book Club Edition or a First Edition. There are signs to look for. A Book Club usually doesn't have a price on its dustjacket. Many Book Club Edtions also have a small embossement at the tail of the back cover. Sometimes there is literally no way to tell for sure except by weight. Book Club Editions must always be noted as such.
- Remainder Marks are put on a book when it is sold off cheaply to a remainder company. These companies sell books for a fraction of their original price, which does not in itself decrease the eventual value to a collector, but the large mark or stamp on the head or tail of the book block does bring down the value.
Just as an aside: a watermark is produced in handmade paper by sewing fine copper or brass thread through the mesh of the mould. When the water drains away the pulp is slightly thinner in the places where the wire sticks up and leaves a relief picture in the paper which can be seen when the sheet is held up to the light.
The book has three edges (as a rule): the fore-edge, the top edge or head, the bottom edge or tail. The spine would be the fourth edge if it did not already have a name of its own.
Like so many elements in book binding headbands are both decorative and structural. Headbands appear at the head and often the tail of the spine. In years past headbands were sewn onto the book block and helped to protect the head of the spine from damage when it was pulled from the shelf. Now headbands are usually woven pieces glued onto the spine as a decorative element.
Let me first say that the following definition is subject to debate.
There is no real consensus on these two terms, but we are putting down the definition which we use and which is becoming more standard in the book trade. The hinge is the place on the inside of the book where the spine and the sides of the binding meet while the joint is the place on the outside of the book where the spine and the sides of the binding meet.
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