Never going to find a universal definition, but my 2 bits:
I would, by modern definitions consider "apps" to be limited use software on limited use devices. Such as the "app" buzzword for smartphones and tablets. I consider iWork, Angry Birds, GarageBand on iOS all "apps", despite them being very different function and purpose wise. I don't use the "app" word for anything other than when in reference to SW on content consumption "appliances" like tablets, personally.
Well, it seems to me that an "app" used to mean an application program - like a word-processor, CAD, drawing program or desk-top publishing program.
The word "app" only came to be applied to those little programs on portable devices when Apple wanted a name for its iPhone programs....and since "app" sounded a lot like their trademark name that's what they went with (you buy "apps" from the "apple store" etc.) Anyway, that's just all theory on my part. But it seems strange to me to call one of those little programs on a cell phone an app...to me an "app" or "application program" always meant those big, serious and expensive programs like the ones I've named above.
