Periodicals are publications that appear "periodically"; they are published at specific times during the year -- for example: daily, weekly, monthly, quarterly (every 3 months) or annually (once a year). The three specific types of periodicals that you will see most often in your research are magazines, journals, and newspapers.
Magazines: Use magazines when you need: up-to-date information about current and general articles written for people who are not necessarily experts in the subject area.
Journals: Articles that appear in journals are generally written by scholars or experts in an academic or professional field. The articles may report original research or cover highly specialized topics; usually long, they provide in-depth analyses, bibliographies of references used in preparing the article, and resources for further study.
Newspapers: Newspapers provide current information about local, regional, national or international events as well as classified ads and editorials.