http://en.wikipedia.org/wiki/Search_engine

http://www.techterms.com/definition/searchengine

http://www.answers.com/topic/search-engine

http://webopedia.internet.com/TERM/s/search_engine.html

http://realestate.about.com/od/sv/g/defsearcheng.htm

http://www.ehow.com/how_5633544_define-seo.html

http://www.wordiq.com/definition/Search_engine

http://www.wordiq.com/definition/Search_engines

http://www.maximized.com/products/flashstats/support/searchengines.asp

http://www.businessdictionary.com/definition/search-engine.html