Drupal has many specific terms that can have different meanings depending on usage (e.g. view vs. a Drupal View). It looks like another in Drupal 8 is plugin & module. Generically, both seem to imply extending functionality to existing code (e.g. FireFox plugin, WordPress plugin, Drupal module, Angular module, etc.). However, it seems like they are 2 different things in Drupal 8.
As I understand it, D8 plugins (the incorporation of CTools plugins in D8?) are reusable components like a form widget, while modules are extensions to Drupal 8 core code that can implement or create plugins. Is this correct?