<p><strong>Noun</strong></p><ul><li>plural: quartos</li><li>a book size of about 9½ × 12 inches (24 × 30 centimeters), determined by folding printed sheets twice to form four leaves or eight pages</li><li>a book of this size</li></ul><p><strong>Adjective</strong></p><ul><li>bound in quarto</li></ul>