The three new deployment models for Apps for SharePoint are the SharePoint-hosted, Autohosted, and Provider-hosted app models.
The Autohosted app model is also used for lightweight apps, but the code for this app is automatically deployed to Windows Azure. You can tap into the power of Windows Azure Web Sites and SQL Database to build data-driven apps. The scope for Autohosted apps is at the site or tenancy level.
The Provider-hosted app model is about power and flexibility. The code does not live in SharePoint, but lives in a separate domain. This could be Windows Azure — in which case you can take full advantage of all of the features of the Windows Azure platform, or it could be IIS (by leveraging the Provider-hosted template in Visual Studio), or even a completely separate PHP app that lives in your own domain-hosted environment. There is quite a bit of flexibility built into this app model, but what comes with it is the need to manage your own code that lives in this separate domain.
These new models are a paradigm shift from previous versions of SharePoint and will surely change the way in which you think about, design, and deploy your apps.
The next chapter explores the SharePoint 2013 developer tooling in greater ...