32mo Definition
noun
(paper) Abbreviation of thirty-twomo; a size of paper cut from standard uncut free sheets, corresponding to such a sheet folded into thirty-two leaves, yielding sixty-four pages when printed on both sides. Page size is dependent on the size of sheet used, with the largest standard size, Atlas (36" by 26") yielding a page size of 6-1/2" by 4-1/2".
Wiktionary
(printing) A book with leaves of such size, about the size of a contemporary trade paperback.
Wiktionary