en.wikipedia.org
en.wikipedia.org
http://en.wikipedia.org/wiki/Search_engine_optimization
moz.com
moz.com
http://moz.com/beginners-guide-to-seo
searchengineland.com
searchengineland.com
http://searchengineland.com/guide/what-is-seo
searchenginewatch.com
searchenginewatch.com
http://searchenginewatch.com/seo
www.google.com
www.google.com
http://www.google.com/webmasters/docs/search-engine-optimization-starter-guide.pdf
www.majesticseo.com
www.majesticseo.com
http://www.majesticseo.com/