Most research databases use a special set of terms called Boolean operators to help you narrow your search results to return only the information that is most useful for your chosen topic or research question. Here are the most common ones, with descriptions of how they will affect your search results.
AND - only returns results that contain both search terms
OR - returns any result containing either search term, or a combination of both
NOT - weeds out all results that include a certain search term
* - (wildcard) captures variations of search terms; a search for teach* would return results containing teach, teaches, teaching, teacher, teachers
"" - placing a term in quotes returns only results that include the whole phrase as typed
() - use parentheses to order your operators (which operators should the search engine pay attention to first?)
Putting it Together
Example query: ((bicycl* OR cycl*) AND inventor) NOT racing
This search would return results that include ALL of the following:
1. One or more of the following: a variation of the word bicycle, a variation of the word cycle (e.g. bicycle, bicycling, cycle, cycling, cyclist)
2. The word inventor
3. No instance of the word racing
***Some search engines have different wildcards (like the * described here) or lack them entirely. Also, some search engines, like Google, substitute - minus sign for NOT. Terms like OR, AND are fairly universal, however, as are "" and ().