I see there are some questions tagged untagged.
What does the tag mean? What should I do when I find questions tagged with that tag?
untagged is a tag that is added to a question for which the existing tags have been removed. This happens when a question is migrated from another site: Every tag not defined from the site receiving the question is removed; if the question is left with zero tag, untagged is added to the question since each question needs at least a tag. (Synonyms are also checked; if the tag used from the origin site is a synonym in the receiving site, the tag will not be removed from the question, but replaced from the master tag.)
untagged cannot be manually added to questions. Any edit adding it will report the following error:
The 'untagged' tag is not allowed.
This is a special tag that is designed to be used only by the system for questions that have had all of their other tags removed. Please use a real tag instead.
untagged is a temporary tag that needs to be replaced with one or more tags defined in Drupal Answers. Check the question (including the question in the original site), and see which of the tags Drupal Answers uses applies to the question; the version tag about the Drupal version probably needs to be added, since tags matching ^drupal-?\d+.*$ are automatically removed when the question is migrated to Drupal Answers.