12mo : An abbreviation for duodecimo, a book size describing a book which is approximately 7 by 4.5 inches.

tight : Used to mean that the binding of a book has not been overly loosened by frequent use.

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.