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Octavo

 Refers to the size of the book; the most common book size since the early 17th century, an octavo book averages about 6 x 9 inches. The term originally referred to the number of folds (8) in a standard book-printing sheet, but it now commonly refers to size.

Offprint

 An excerpt of a larger publication that has been printed and bound separately for promotional purposes. For example, publishers will print and bound a chapter of a book to send to booksellers or for the author to give away before the entire book is published. Scholarly excerpts are another example; a portion of a large journal piece printed for a professor to distribute. Offprints are highly sought after by collectors because, technically, they can be considered a first separate edition of the work and will often have a presentation inscription.

Offset

 The light image of transferred ink or an imprint that comes from an adjoining text page or illustration, or an inserted paper. This transference is not done on purpose and can be caused by humidity, acid from the inserted paper, or wet ink when the book was bound.

Offset

 The light image of transferred ink or an imprint that comes from an adjoining text page or illustration, or an inserted paper.

Out Of Print

 a title no longer maintained in the publisher's catalogue or inventory

Out Of Print (Op)

 A publication that is no longer available through the publisher.

Out-Of-Series

 Unnumbered editions from a numbered limited edition series. They are considered "extra copies" of the edition, are usually not signed, and are not considered part of the limited edition series.

Overrun

 To print a larger quantity of books than ordered. Printers estimate a 10 percent spoilage. If this does not occur, the additional books are charged to the customer but only up to 10 percent.