I write CGI applications. Occasionally, I write CGI scripts, but most of the time, I just use something that someone else wrote, or that I wrote a long time ago. A CGI script is distinguished from a CGI applications in a number of ways. Most of these would be, I would think, evident to someone with some Unix experience, since that distinction is made in the Unix world. Scripts are tiny bits of code that perform a small number of trivial functions.
Applications are things that are of rather larger scope.
They have a distinct purpose. They store and retrieve data. They have a lifetime somewhat longer than the typical one or two page views that constitute the life cycle of a form-handler script. Obviously, this distinction is very subjective and vague. The first person that wrote and distributed real CGI applications, at least that I was aware of, was Matt Wright.