Also known as Boolean operators, connectors are used in keyword searches to link together two or more terms.
The most commonly used connectors are AND and OR.

AND narrows a search; you get fewer records, because both concepts must be present in the records found--here the area is in yellow. Use AND to combine different concepts in one search.

OR broadens a search; you get more records because OR includes each of the concepts separately, as well as both concepts when found together. OR is often used to link together related concepts. 

NOT is often used in conjunction with AND to exclude unwanted results.