"Boolean" search terms (named for George Boole, 19th century English mathematician) refer to the usage of and, not, and or to unite keywords in search strings. The different terms return different results:
A AND B = The narrowest: Results that only include both keywords A and B
A NOT B = Results that include A except where B is also mentioned
A OR B = The broadest: Everything that mentions A and everything that mentions B
Civil War –site:wikipedia.org
Site: only search on certain sites:
link: search for sites link to a certain URL
* (asterisk): use as a place holder for an unknown word or term. Also called a wildcard.
four *, seven years ago
Info: Get information about the url and related sites to your search. Can include cache information too.
Filetype: look for a particular type of file like pdf, jpg, png, etc.
non-hodgkins lymphoma filetype:pdf
Intitle: Look for a word in the title
You can combine any of these operators with a space to get results:
author: andrew russell intitle: networking filetype:pdf
Guides from the databases themselves on how to use them more efficiently.