A periodical is any publication that is issued in regular intervals (daily, weekly, monthly, etc.).
This includes newspapers, magazines, trade publications and scholarly or academic journals. Use the side menu to learn more about each type of publication and to find links to databases containing each type of article.
It is important to be able to correctly identify the articles you are using and to know how to use them in the appropriate contexts.
If you are writing a serious essay, you probably want to consider using academic journal articles.
If you're investigating current events, you could consider using newspaper or magazine articles.
Also keep in mind the assignment you are working on and what you've been asked to do. Have you been specifically asked to use a certain type of article? (i.e. one that is peer-reviewed?). Always use the type of sources requested by your instructor or identified in your assignment.