Metadata
The literal meaning of "metadata" is "data about data". It was originally intended to provide a snapshot of what a webpage's content was actually about, by highlighting to the search engine spiders the page's most relevant categories of subject matter.
Back in the days when AltaVista was the king of the search engines, however, it became easy for search engine optimisers to "fool" the spiders into believing a webpage was about something other than the actual content on the page. This was achieved through techniques such as "keyword stuffing" the keywords and description meta tags with irrelevant, but more popular phrases, that would ensure the page was listed for popular searches - thus driving more traffic to the site.
Since the rise of Google as the dominant search engine, though, metadata is not so important for optimisation purposes as it was before. There are essentially 3 key elements to metadata worth considering:
1) This is the series of words that appears in the blue bar at the top of a person's browser screen in Internet Explorer.
This is still a key factor in determining search engine rankings, and should be a part of any "on-page" optimisation programme.
In a maximum of 9 words, you should echo the page's main target search phrases (see the Keyword Research and Text Content sections) here.
This will also become the headline that is featured in the SERPs, so it should be eye-catching as well as relevant.
2) Inserted between the tags - this is occasionally used as the snippet of information underneath the headline in the SERPs, so should again be relevant to the page's content. This should be a proper sentence, in 21 words or less.
3) Almost totally ignored now, but doesn't harm rankings if included.
