I have been reading quite a lot about SharePoint 2013/2016 lately and I am not sure I am able to see the difference between Farm Solutions and Provider Hosted App. Please correct me if I am wrong:
Farm Solutions are custom code deployed directly on the SharePoint Server (They are Full trust Applications), but then I can't see the difference between sandboxed and Farm Solutions.
Provider Hosted App are applications that can be hosted on a complete different server and have to use S2S identification in order to be able to connect to the SharePoint Server (There are High Trust, user need to say he trusts this application) and are displayed in an IFrame to have a seemingly SharePoint experience using Chrome styling.
The more I read, the more I am confused!