Customer reviews for app.

Yes, you are correct. If you need to have a store of data like reviews which all of your app's users can contribute to and view, this data needs to be accessible to the users' devices, usually on a server on the internet. The iOS track will teach you how you can use an app to fetch data from a server with an API. If you look at other courses on Treehouse, you'll see there are lots of different ways you can create the API on the server side.

MySQL is useful as a database but you generally wouldn't want a mobile app to connect to it directly. You'd usually create some form of server API which would use the database to store its data and have your mobile apps access the API. That way, if your backend system needed to change at some point in the future, as long as the new version supplies an API with the same specification as before, your apps would not need to be changed.