Boolean search allows to lookup pages containing some word and not containing other. To express the fact that a page must contain a word, a + sign must be placed in front of the word. To search for all pages not containing a word, a - sign should be used. For example, you can search +net -"Internet" which will show pages containing net , network , etc., only if they don't contain Internet . Note that searching for -word or +foo -foo will produce no results.
Refined boolean search can be done by mixing a boolean expression with normal words. Searching +net +Foo bar will sort results showing pages containing net , Foo and optionally bar first.