Agustin V. Zamorano, architect

MM : Mass Market Paperback. Often thought of as the pocket paperback.

wrappers : Paperback or softbound. Also, wraps.

4to : Or quarto. A term used generally to describe the approximate size of a book, a book that is about 10" to 12" tall and roughly squarish in shape. The term is based on the size of paper traditionally used by book printers which has been folded and cut into 16 pages.