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Mass market paperback : Also known as the pocket paperback. A small format paperback usually measuring about 4" by 6".

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trade paperback : Often used to indicate any paperback book that is somewhat larger than a mass-market paperback.

As New : "the book is in the same immaculate condition in which it was published. There can be no defects, no missing pages, no library stamps, etc., and the dust jacket (if it was issued with one) must be perfect without any tears." Condition definition from AB Bookman's Weekly.