Invented by George Boole, these terms enable combinations of words to be searched at one time with different results, depending on the Boolean operator used. The standard terms are AND, OR, and NOT.
As this is counter-intuitive to natural language that we use in everyday speech, if you get confused, consider this phrase: OR IS MORE
This enables multiple forms of words to be searched at one time. To capture all of them at once, you insert a "truncation" symbol after the "root" of the word. This principle works in many databases, although the symbol for truncation may differ from database to database.
Example: chromato* retrieves "chromatograph," "chromatography," "chromatographic," "chromatogram," "chromatograms," etc.
To make sure two words are adjacent in your search results, use quotation marks, e.g.
"acid rain" or "risk analysis"
Getting only peer-reviewed articles
Many of the databases have a limiter so that you can search for only peer-reviewed articles. Peer-reviewed articles are also called scholarly or academic, depending on which database you are using.