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.
Full copies of Drupal that include Drupal Core, along with additional software are called, in Drupal terminology, distributions.
Use it for the module for running a group of affiliated sites from one installation and a single shared database.
Use it for Drupal 8 plugins; for plugins implemented from the Views module use views, ctools for Chaos tool suite plugins.
Use it for questions about moving from a major release of Drupal to the next.
The act of saving files, data, or applications to a secondary media is called backing up.
Use it for the service that provides payment processing for e-commerce transactions.
Use it for questions about the settings that can be retrieved with theme_get_setting(). Don't use it for generic settings.
Use it for questions about various types of logs in Drupal, including the ones shown in /admin/reports.
Use it for questions on the module which allows users to earn and use points through various activities: the Userpoints module.
Use it for questions about the services provided by Drupal.org.
Drupal has modules for either helping advertising or blocking unsolicited advertising posted as comments or nodes.
Use it for questions about modal popup dialogs, including the overlay implemented in the Drupal 7 Overlay module.
Use it for questions about the core API that allows developers to split a big task in several minor chunks or batches.
Use it for questions about selecting or using any of the charting 'modules' and/or charting 'libraries' in Drupal.
A specially written PHP callback whose parameters are configured through the web is, in Drupal terminology, an action.
Use it for questions about the suite of modules for managing content inside Drupal: the Workbench project.
Use it for questions about deployment: staging content, managing and syncing sites across multiple servers.
Privatemsg allows your site's visitors to send private messages to each other.
Use it for questions related to physical printing of content.
Use it for questions about Google Analytics integration with Drupal website.
Installation profiles combine core Drupal, contributed modules, themes, and pre-defined configuration into one download.
The process to merge files together to improve a site performance with less server requests is called file aggregation.
Use it for questions about the queue of messages displayed to the client.
Drupal allows a restrict set of users to access the site when maintenance tasks run: the maintenance mode.
Use it for questions related to the Group module, not the Organic Groups module.
Use it for questions about the Drupal Bootstrap base theme.
Use it for questions about the set of Drupal modules that helps you maintain your Drupal sites: Aegir.
A challenge-response test used for determining human users is called CAPTCHA.
Use it for questions about the free Mac or Windows based AMP made available from Acquia.
Use it for questions about HTTP requests, sending and receiving requests, status codes and more.
Use it for questions about the operations done from Drupal to initialize itself, not about Twitter Bootstrap.