Metadata is used to describe the contents of a page. In the past, metadata played a key role in helping search engines understand the nature and content of pages, but today it plays a less critical role. Despite its decreasing importance, metadata should never be ignored; it is the one technical feature of pages that is purely intended to help understand and categorize the page content and therefore should always be used to further your SEO goals.
Metadata is added to pages through the use of meta tags, which appear in the head of the HTML document. While the W3C metadata standards provide for a wide range of possible meta tags, you will need to install an extension to fully control the metadata of your Drupal site. Different modules give you different options, but the key tags you will want to implement on your site are shown in the following table: