Horace's rule for distinguishing between an app and a service works only in the simplest cases. It ignores things like Facebook Connect or "Connect with Twitter". It also ignores pure-advertising based experiences such as American Idol. The American Idol app on iOS does not require you to enter a pw/username.

Also, both app and service tend to imply one-to-one relationships.

In reality the 'new world' is composed of 'apps' that are client front-ends to back-end services that are actually composed of multiple services from 3rd parties that pull content from multiple sources and are made available via multiple channels and represent and re-enforce one or more brands.

These are some of the reasons why I decided to use a different term than either app or service: Experience.

An end-to-end user experience is a cohesive combination of devices,people, brands, channels, services, and content that improves over time.

Or, more succinctly, Experience equals stuff over time (exp = stuff/time).

Oh, how I love this line:

"The lowly app coupled with cloud-based services[1] is the termite that is set to eat the foundations of the largest of the industries still standing."

The computing industry has been defined as a series of stair steps, each comprising a radical disruption, with consummate growth in the size of the industry, the profits, and advancement of technology. Mainframes → Minis → PCs → GUI → Web → Mobile.

What's next? I assert it is Experiences.

http://ceklog.kindel.com/2012/04/02/experience-stuff-time/