>I would like to have a real understanding of what one is...

better luck next time, but.

app /ap/ n. Short for `application program', as opposed to a systems program. Apps are what systems vendors are forever chasing developers to create for their environments so they can sell more boxes. Hackers tend not to think of the things they themselves run as apps; thus, in hacker parlance the term excludes compilers, program editors, games, and messaging systems, though a user would consider all those to be apps. (Broadly, an app is often a self-contained environment for performing some well-defined task such as `word processing'; hackers tend to prefer more general-purpose tools.) - the jargon dictionary