Q. What's the difference between periodicals, journals, magazines and newspapers?

A periodical is any publication that comes out periodically, including journals, magazines, and newspapers. 

An academic journal is a periodical aimed at scholars, academics, and researchers, usually written in technical language by experts on the subject. They contain original research, conclusions based on data, footnotes or endnotes, and more often than not include an abstract and bibliography. Many, but not all, academic journals are peer-reviewed. A few examples are Journal of Advanced Nursing, Shakespeare Quarterly, and Nature.

A magazine is a periodical aimed at a specific audience, covering recent issues and specific subjects through articles, interviews, and personal narratives. Articles are often written by professional writers with or without expertise in the subject and contain "secondary" discussion of events, usually with little documentation (e.g. footnotes or bibliography). Magazines use vocabulary understandable to most people, and often have lots of eye-catching illustrations. Some examples are National Geographic, Time, and Popular Mechanics.

A newspaper is a periodical aimed at the general public, covering recent issues and news in a formal, brief, and objective matter. A few examples are New York Times, Wallstreet Journal, and The Commercial Appeal.