Simple question: What is an Application? But is the answer equally simple?

Maybe I´m naive or dumb, but the more I think about it, the less I know what an "application" - an application in software development - is. Can you help me? Who can give me a simple answer?

Is it a single EXE assembly? No, not necessarily.

Or is it an EXE together with all the other assemblies I write? Hm, maybe.

Is a service (as in SOA) an application?

What is a distributed application? Is it one application whose parts run on different machines? Or are these parts in themselves applications?

If I start out with a single EXE to solve my problem and later decide to split it in two: do I then have two applications? Or is it still one application which incidentally manifests itself as two EXE files?

You see, I´m somewhat confused. The more so, because when I turn to current architecture models (e.g. layered architecture, or Clemens Vaster´s onion) I don´t find an answer. Neither helps a definition like "application program".

It seems the term "application" is either overloaded with many meanings. Or it is underspecified.

But maybe someone out there can provide a (link to a ) consice definition?