Boolean logic defineds logical relationships between terms in a search. The Boolean search operators are and, or, and not. You can use these operators to create a very broad or very narrow search.
AND combines search terms so that each search result contains all of the terms. For example, travel and Europe finds articles that contain both travel and Europe.
OR combines search terms so that each search result contains at least one of the terms. For example, college or university finds results that contain either college or university.
NOT excludes terms so that each search result does not contain any of the terms that follow it. For example, television not cable finds results that contain television but not cable.
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Source: Excerpt from EBSCO