What is a Periodical?
Magazines are periodicals. Newspapers are periodicals. Why do librarians call themperiodicals? It's our business to collect and provide access to all kinds of publications. We use the word "periodical" to distinguish publications that are issued periodically--daily, weekly, monthly, quarterly--from publications that are issued singly, like books.
Newspapers and magazines
Librarians and publishers call newspapers and magazines "popular" periodicals.
Journals
Journals are also often called academic or scholarly to indicate both their origins (often in academic institutions) and audiences (often scholars). They are also often peer-reviewed or refereed.
People new to these terms often confuse journal with article. An article is a single authored item within any kind of periodical. A journal is a periodically-published collection of articles by different authors.
There is more information about Periodicals and how to distinguish between types of them on the following guide: