In addition to the "AND" and "OR" conditions, some search engines offer a third option - "NOT".
When you type in a word and mark it as "NOT", the search engine will ignore any document that includes this word.
The "NOT" condition is always used in addition to other "AND" or "OR" condition, and it is recommended to use this option very carefully, since it might aliminate usefull documents from the results list.
