octavo : A book whose page size is approximately 12 inches by 9 inches. The size is based on a sheet of paper 25 inches by 38 inches, the size of paper traditionally used by book printers, which has been cut into eight pages.

remainder mark : Usually an ink marking of some sort which indicates that the book was designated a remainder. In most cases, it can be found on the edges of the text block in the form of a marker stripe or a stamp of some sort.

Remainder marks considerably lower the overall collectibility of a title, although, in some cases, they are acceptable to a collector.