Definitions for "Octavo"
A book composed of sheets each of which is folded into eight leaves; hence, indicating more or less definitely a size of book so made; -- usually written 8vo or 8°.
Having eight leaves to a sheet; as, an octavo form, book, leaf, size, etc.
Refers to the size of the book, usually 6 x 9 inches. Octavo, also referred to as 8vo, is the most common size for modern hardcover books.