Boolean operators use AND, OR, NOT to limit or expand a search. (Note the capitalization. Many databases require operators to be in all caps, as do search engines like Google, which also allows for Boolean based searches.)
In other words, the search results will contain search term X and search term Y.
In other words, the search results will contain search term X or search term Y or both.
In other words, the results will not contain search term X.
Boolean operator searches can be simple, e.g., Moose AND Elk; Moose NOT Elk. Or they can be more complex and nuanced when combining operators and use parentheses, e.g., (Caribou AND Elk) NOT Moose; (Moose OR Elk) NOT Caribou.
The design of this page was partly adapted from Research: By Course, Subject, or Topic, by University of Arizona Libraries, © 2020 The Arizona Board of Regents on behalf of The University of Arizona, licensed under a Creative Commons Attribution 4.0 International License.