I don't know if this is the right kind of question to ask here or not. I read that Instagram uses django which is a python web framework. But Instagram is an iOS application. Aren't iOS apps written in objective c? What do they mean by Instagram uses django?
IOS is the "Frontend" of the application. Django is a backend "Server Side" Web Framework.
For example, if there is an iPhone application that shows you all the latest tutorial videos about baking (lets say you had a website bakingtutorials.com), you would make an iPhone application in objective-c to run as the frontend. In your objective-c iPhone code, you would communicate with a "server" which runs Django/Python. The Server Side (Django) holds the video and other baking data in a database. The Frontend iOS application requests data from the Django application. Client Side & Server Side communication. This is usually accomplished with a RESTful API - which in basic terms, means the iPhone application uses human-readable URLs to grab data from Django/the server's database. This data is sent to the frontend from the server where it is parsed by objective-c and formatted for the application