Any web page, including one generated by Joomla can have "meta tags" or "elements" in the header information. The one's that get the most focus are the Title tag, the Description tag and the Keyword tag. This is mainly because it's thought that these have the most influence on Search Engine Ranking (which is not entirely true).

There are other tags/elements such as robots or language that provoke less discussion that the title, description or keyword, but are still important.

Lets take each Tag in turn and see how they are used in Joomla.

Read original post at source site... http://www.compassdesigns.net/joomla-blog/how-google-uses-joomla-meta-title-description-and-keyword-tags