Drupal comes bundled with a content tagging functionality . The system allows you to create tags either before, or during, content creation and associate those terms with content items. The tags can also be grouped together into "vocabularies".
Tagging provides a useful way for your site visitors to discover and access related content. Tags also create useful SEO opportunities; use them to add keyphrases and related concepts to your content items. Going further, in Drupal, it's easy to create menu items from your tags, allowing you to build pages that contain all the content items that have been tagged with a particular term. When you combine the ability to create tag pages with the functionality of the path module, you wind up with a great way to produce URLs and content pages that solidly reinforce your keyphrases strategy.