title: Use of ._meta Django
body: <p>I want to ask about the use of ._meta in this code ? I didn't find a documentation that explains the use of .meta </p>
  
  <pre><code>def resend_activation_email(self, request, queryset):
      """
      Re-sends activation emails for the selected users.
  
      Note that this will *only* send activation emails for users
      who are eligible to activate; emails will not be sent to users
      whose activation keys have expired or who have already
      activated.
  
      """
      if Site._meta.installed:
          site = Site.objects.get_current()
      else:
          site = RequestSite(request)
  
      for profile in queryset:
          if not profile.activation_key_expired():
              profile.send_activation_email(site)
  resend_activation_email.short_description = _("Re-send activation emails")
  </code></pre>