A "periodical" is any publication that comes out regularly or occasionally (i.e. periodically, get it?). TV Guide, Sports Illustrated, The Journal of Anthropological Research, The World Almanac, and the phone book are all periodicals.
A "magazine" is a periodical with a popular focus, i.e. aimed at the general public, and containing news, personal narratives, and opinion. Articles are often written by professional writers with or without expertise in the subject; they contain "secondary" discussion of events, usually with little documentation (e.g. footnotes). Magazines use vocabulary understandable to most people, and often have lots of eye-catching illustrations. Time, Newsweek, U.S. News & World Report, and Psychology Today are magazines
A "journal" is a scholarly periodical aimed at specialists and researchers. Articles are generally written by experts in the subject, using more technical language. They contain original research, conclusions based on data, footnotes or endnotes, and often an abstract or bibliography. The Journal of Physical Chemistry, The Chaucer Review, The Milbank Quarterly, and Labor History are examples of journals.
It's important to understand the differences between journals and magazines. Magazines are not necessarily bad or low quality (nor are journals necessarily high quality) -- they simply aren't designed to support most upper-level academic research. This is because they don't document their sources of information, and they generally lack the depth of scholarly journals.
The table below highlights the differences.
Journals - Scholarly Magazines - Popular
Content Detailed report or original research or experiment. Secondary report or discussion; may include personal narrative, opinion, anecdotes
Author Author’s credentials are given; usually a scholar with subject expertise Author may or may not be named; often a professional writer; may or may not have subject expertise.
Audience Scholars, researchers, and students General public; the interested non-specialist
Language Specialized terminology or jargon of the field; requires prior knowledge Vocabulary in general usage; understandable to most readers
Layout & Organization Formal organization often begins with an abstract of the article; if reporting experimental findings notes the experiment’s purpose, methodology, and analysis of the results; a conclusion, and a bibliography; may include charts or graphs, but rarely photographs. Informal organization: eye-catching type and formatting, usually includes illustrations or photographs. May not intend to present an idea with supporting evidence or come to a conclusion
Bibliography & References Required. All quotes and facts can be verified. Rare. Scanty, if any, information about sources.
Examples Developmental Psychology
JAMA: Journal of the American Medical Association
The words "journal" or "review" often appear in the title Harper’s
Newsweek
People
Time
Almost anything available in a store or news stand.