SEO is an abbreviation for ‘search engine optimization’ . This means optimizing a website for appearing as high as possible in search results (SERPs – Search Engine Results Pages). Here are some cool resources about this topic:
http://en.wikipedia.org/wiki/Search_engine_optimization – Search engine optimization on Wikipedia.org. This is a nice and detailed article about this technique.
http://support.google.com/webmasters/bin/answer.py?hl=en&answer=35291 – here is another good article on Google’s support pages. It’s very good for people who has just begun with their SEO efforts.
This is another cool topic about the matter: http://www.webconfs.com/seo-tutorial/introduction-to-seo.php