[Django]-What is a "django backend"?

django comes with one or more implementations of authentication, caching, etc but the framework anticipates the need for adding your own custom “backend” implementation. They generally provide a simple well-documented interface as well as a setting variable so it is easy to plug in your own custom module.

This term/pattern is also used by common django apps such as django-registration.

If you are into design patterns this blog provides some analysis: http://charlesleifer.com/blog/django-patterns-pluggable-backends/