Peer Reviewed Journal - A publication, usually scholarly, in which articles are reviewed by a panel before being accepted for publication. Also sometimes called scholarly or refereed.

Periodical - Any publication printed on a regular, predictable schedule. A periodical may be published weekly, monthly, quarterly, etc. 
See Also: Journal, Magazine, Serial

Periodical index - A subject listing of what articles have been published in what magazines and journals. Some periodical indexes are general in scope and others are subject-specific.

Phrase searching - Allows you, in a database, to search for particular words in a particular order. Useful for proper names, names of companies and names of government departments. Most phrase searches should be in quotations, such as "Department of Justice".

Plagiarism - Stealing someone else's ideas or information and presenting them as your own.

Popular sources - Popular sources are books and magazine articles written for the general public. See Also:Scholarly sources, Trade publications

Primary sources - Primary sources are results of experiments or original research, literary works, autobiographies, original theories, and other materials. 
See Also: Secondary sources

Proximity - Some search tools use proximity of two or more search terms to determine relevancy of a result.  Proximity operators specify how far apart matching words can be. They may also specify word order. Details vary considerably from system to system.