Periodicals are publications that come out on a regular schedule. They include different types of magazines, journals, trade publications and newspapers. Periodical articles are often the best sources for research, especially if your topic requires primary sources, recent information, or detailed information. Information appearing in periodicals constitutes the bulk of published information and unlike a majority of the information on free websites, the information in periodicals has been reviewed by peers or by another evaluation process.
There are four main categories of periodicals: 1) scholarly journals, 2) trade/professional journals, 3) popular magazines & newspapers, and 4) sensational magazines.
The format of periodicals can be print or electronic. Electronic periodicals can be ones that are only published electronically and ones in proprietary databases that appeared originally in hardcopy format.
Source: Research Minutes: How to Identify Scholarly Journal Articles. Olin Library. Cornell University. 28 Feb. 2008 http://www.youtube.com/watch?v=uDGJ2CYfY9A