Boolean searching is built on a method of symbolic logic developed by George Boole, a 19th century English mathematician.
Boolean searches allow you to combine words and phrases using the words AND, OR, NOT (known as Boolean operators) to limit, broaden, or define your search. A good researcher should know how to do a Boolean Search.
AND : Using AND narrows a search by combining terms.
OR : Using OR broadens a search to include results that contain either of the words you're looking for.
NOT : Using NOT will narrow a search by exclusion. (Some search engines, like Google, recognize the minus (-) symbol, instead of the word NOT).
Quotations : Placing quotations around a specific phrase will help you narrow results in order to find information containing that exact wording.
Boolean Searching on the Internet
Power Searching with Boolean