The word "periodical" is a generic name for anything that comes out on a periodic basis -- magazines, journals, newspapers, newsletters, etc.
Remember that looking up a periodical in the library catalog only tells you whether the library owns a particular title, like Psychology Today. It doesn't tell you what articles are INSIDE the individual issues of the periodical. For that you will need to look in a periodical INDEX.
There are two primary catagories of periodical indexes: print and online. We have discussed both in some detail. However, if you are not yet familiar with print indexes, be sure to go to a library near you and use the Wilson Indexes of the appropriate subject area to research your term paper. Have the librarian answer any questions you may encounter.
Remember that I said near the beginning of the course that print indexes are where you should start narrowing your topic and doing your research. If you haven't done it yet... do it now.