Use of "class Meta" in Django's admin.py

Can someone please explain why we use nested meta class here? I understood why we use Meta class in model.py from "https://docs.djangoproject.com/en/1.9/topics/db/models/#meta-options" but I can't understand why we use it in admin.py and forms.py classes as shown below:

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)