When people refer to an architecture that involves a single service API that all clients talk to (a client can be an iPad app, etc), what is the "client" for the web app -- is it

A) the web browser itself. Thus, the entire app is written in html/css/javascript and ajax calls to the service are made to fetch data and changes are made through javascript

or

B) you have an MVC-like stack on a server, only instead of the controllers calling to the model layer directly, they call to the service API which return models that are used to render the traditional views

or

C) something else?