Everyone talks about content being a key to better search engine ranking but very few can explain why content is one of the primary factors considered by a search engine algorithm before assigning a high search engine ranking to a site.

The reason that one hears most of the time is that search engines want to give more importance to visible factors (i.e. factors like text that are visible to a human) and hence good content in the form of visible text on the web page helps in improving the search engine ranking of that page.

This explanation is not incorrect. In fact this is quite an accurate explanation for most people. But then you need to put on an engineer's hat and ask Why? and How? Does textual content helps from an SEO perspective to attain better rankings on search engines.

The key lies in AI (artificial Intelligence) and more specifically semantic nets. The search engines nowadays use these principles while crawling the web to index pages.

Using semantically related terms on a page allows you to build a theme and helps you to associate your page with other pages related to the same topic. This helps your page rank for many long tail keywords. Creating a theme does not mean only presence of keywords on the website that count but all the content on the page which determines what the page is about.

Links from such semantically related pages helps search engines to classify website according to information and content provided on it. Stemming is used to find increased relevance in the content of the site. A mesh of links from relevant sites creates a semantic net for a certain topic.

This helps in ranking the website ranking on search engines for relevant keywords.

Search engine optimization is a long-term solution to your traffic woes. Search engines often change their algorithms. Hence you need to tweak your website to compensate of the changes, thus enabling you to stay on top.