Keyword phrases are the words and control symbols used as query input for a database search. They are most commonly used in reference to web page search engines where the keywords describe the content the searcher is seeking.
Many public SE's support more advanced boolean searching through control symbols. For example in the the phrase
'Paris Texas' -France
the quotes and minus symbol are control phrases. The example looks for pages where Paris and Texas appear together but does not have the term France in the text.
- Most searches on the Internet use two to three words without boolean control.