An application is a collection of programs and/or libraries that are intended to provide a complete toolset for a certain activity, i.e., document or image editing. Application suites are even more broad in scope, attempting to provide complete solution for a broader and more general activity, such as office operations or film production.
Richard Suchenwirth 2007-05-12: I'm a bit puzzled why some people are so much concerned with "applications". In my younger days, I think they were just called "programs"; these days, and done in Tcl/Tk, shouldn't one just call them "scripts"?
I know there are some monstrous "applications" out in the world, e.g. Microsoft Word comes to mind - a plethora of bells and whistles, that need their own training classes.
But comparing what users want and what they get, one cannot really call it a 1:1 mapping.
In new situations (like in research & development), chances are even less that there is one "application" that covers the specific needs. So when I need a "program", I rather tailor-make it to suit my needs, rather than download various "applications" to evaluate, and typically find out they offer too much (of what I don't need) and too little (of what I need) at the same time.
I much rather use powerful packages (e.g. tdom for XML, Img for image converters) and glue them together to do just what I want. And I don't call the outcome "applications" - just "scripts". :^)