SEO stands for Search Engine Optimization. Search engines such as GOOGLE send out programs called Spiders or Bots that "crawl" around the web gathering information about the pages that they encounter. These bots bring back the information, often weeks later, to the search engine where the information is indexed. There are proprietary algorithms that the bots use to make decisions on what it is collecting from the visited sites. For example, if a page uses frames the bot stops looking at the page and moves on to the next. What the bots are looking for are well formed pages that use tools like CSS and XHMTL. These are known as Search Engine Friendly pages and get indexed higher. Using those tools and avoiding frames are 2 ways to achieve a higher SEO.