- The page size obtained by folding a whole sheet into four leaves.
- A book composed of pages of this size.
- A size of book in which the leaf is one fourth of a described or implied size of paper.
- Noting the size of a book in which a sheet makes four leaves: as, a <em>quarto</em> volume; being of the size or shape of the leaves of a quarto; as, <em>quarto</em> paper; a <em>quarto</em> edition.
- Having four leaves to the sheet; of the form or size of a quarto.
- Originally, a book of the size of the fourth of sheet of printing paper; a size leaves; in present usage, a book of a square or nearly square form, and usually of large size.
- A size of paper (7.5"-10" x 10"-12.5")(190-254 x 254-312 mm). Formed by folding and cutting one of several standard sizes of paper (15"-20" x 20"-25")(381-508 x 508-635 mm) twice to form 4 leaves (eight sides).
- A book size, corresponding to the paper size.
- the size of a book whose pages are made by folding a sheet of paper twice to form four leaves