new book; newly published book
Literal use for a new book or new publication. In many modern contexts 新刊 or 新刊書 is clearer for this meaning, because 新書 often suggests the paperback format.
That shop handles not only old books but also new books.
shinsho paperback; compact 17-by-11 cm paperback
Publishing-format sense, referring to a small paperback size also called 新書判. Common with nonfiction and general-interest books sold in series.
See also: 新書版
I read a compact paperback on history during my commute.
For this topic, it is a good idea to start with an introductory shinsho paperback.
The researcher published a shinsho paperback about history.
It was decided that the popular series would be released as a shinsho paperback.