A tag is a keyword or label that categorizes your question with other, similar questions. Using the right tags makes it easier for others to find and answer your question.
Use it for questions about the Scald project and related modules.
Use it for the format that allows an embedded representation of a URL on third party sites.
Use it for the event management module for Drupal 8 created in the spirit of the Entity Registration module (Drupal 7): the RNG module.
Use it for customer relationship management integration with Drupal.
Use it for questions about the Mobile tools module.
Use it for questions about logging activity using the Heartbeat module.
Use it for questions related to using Drupal in conjunction with Google Search Console.
Use it for questions about the Pathologic module.
Use it for Drupal questions about Hudson, now Jenkins.