Journal articles are peer reviewed before they are published; magazine articles are not.
It depends on the book's publisher. Some publishers peer review book proposals or books before they are published. Such publishers include
A book does not include a statement that it was peer reviewed. To determine whether or not a book was peer reviewed it is necessary to consult a publisher's policy or ask a librarian.
It is an article that was sent to experts for review before it was published. The experts are the author's peers in their field of study. These peers are also called referees; a peer-reviewed journal may also be called a refereed journal. Often expert reviewers will suggest improvements to articles before they are published.
"Editors of scientific journals send papers out for formal evaluation of their intellectual merit by the authors' scientific peers — other scientists, typically anonymous — who work in the same or a closely related field. Peer review is a kind of scientific 'natural selection'; papers that can withstand the scrutiny of this process will find their way to publication and are often substantially stronger for it. Papers that cannot are rejected. Of course, the authors may have the opportunity to resubmit after making further revisions, or they may try their luck by submitting to another journal.
Peer review does not necessarily determine whether the conclusions of a particular study are correct; that may ultimately require further work that either confirms or refutes the conclusions. Instead, the peer review process is designed to prevent the publication of papers so obviously flawed as to be clearly invalid with regard to the claims made or conclusions drawn, and unlikely to add usefully to the scientific discourse” (Mann, 2014, pp. 78-79).