Periodical: A publication containing articles written by more than one contributer, issued at regular intervals (daily, weekly, monthly, etc.)

• Popular magazines & newspapers are written for a wide audience. Authors of articles may be indicated or not, and articles may be written by journalists, staff, or freelancers. Only occasionally, will experts write for popular magazines & newspapers. Popular magazines and newspapers usually contain a wide variety advertising for products and services.
  

• Professional or trade magazines are aimed at practitioners in a specific profession. The articles are often written by people with experience in the specified professions. They may contain employment ads along with ads for products and services geared toward the corresponding profession.
  

• Scholarly or academic journals are published for scholars and professionals. The authors are almost always scholars and professionals. Contents are reviewed and corrected before publication ("refereed" or "peer reviewed"). Articles contain a list of references and often report the results of a research study. Generally, there is no advertising within scholarly/academic journals.