Applications are the grouping of compiled, executable code and data files in a bundle given the .app filename extension. When you write a program in Cocoa, you are writing AnApplication.
…unless you’re writing aTool, which is really still AnApplication but not according to the ProjectBuilder template.
Tools typically aren’t in a bundle - they’re just a standalone executable in your build directory rather than a bundle folder hierarchy. Plus applications (usually) have a UI, and tools don’t. If tools are not applications though, then it’s not always true that when you write a program in Cocoa, you are writing AnApplication.