Appatic

The answer is: Pretty much everything on/from the web is now a app in one way or another.

Be it a service, a add-on to a service or a service solution to another service. There are many examples and the most common one could be search.

Search is App because it process your query for what you are looking for and delivers you a response in specific pre-defined way from which you go elsewhere. It is utilitarian.

If it delivered what you were looking for depends on both if you used it well and if the search engine actually knows what to display based on what you searched for.

But that is beyond the point.

The only thing is to categorize and tag what kind of App is something and how is distributed.

App as a Solution/Service-Service/Solution as a App. Kind of a chicken-egg dilemma when it comes to start ups today. You get the idea from my petty rationalization.

Most of the times over simplifying or over generalizing is bad in this case is just a point.