title: Use of "class Meta" in Django's admin.py
body: <p>Can someone please explain why we use nested meta class here? I understood why we use Meta class in model.py from "<a href="https://docs.djangoproject.com/en/1.9/topics/db/models/#meta-options" rel="nofollow">https://docs.djangoproject.com/en/1.9/topics/db/models/#meta-options</a>" but I can't understand why we use it in admin.py and forms.py classes as shown below:</p>
  
  <pre><code>from django.contrib import admin
  
  # Register your models here.
  from .models import SignUp
  
  class SignUpAdmin(admin.ModelAdmin):
      list_display = ["__unicode__", "timestamp", "updated"]
      class Meta:
          model = SignUp
  
  admin.site.register(SignUp, SignUpAdmin)
  </code></pre>