Articulate distinction between "library" and "application" projects

There is a distinction between "library" projects and "application" projects that I only recently became more clearly and consciously aware of. For example, see: http://www.fullstackpython.com/application-dependencies.html

The installation and distribution procedures in these two cases are somewhat different. For example, on the packaging and distribution side, it seems libraries should normally use setup()'s install_requires argument, while applications can use requirements.txt, for example.

I think it would be good if the User Guide started articulating this distinction (e.g. in the glossary), so that it can eventually be made more clear which use cases the different advice in the Guide applies to. (For example, I think most of the advice in the tutorials is for installing and packaging libraries rather than applications, even though the language uses the more general term "project.")

This is a bit related to the following (but more general): https://github.com/pypa/python-packaging-user-guide/issues/10

Start by reading the User Guide, especially its glossary and the tutorials that discuss installation and packaging, then compare the library and application guidance described in the issue. Clarify the distinction and indicate which advice applies to each project type, while considering the related issue about broader project terminology. Done means the User Guide consistently communicates these use cases.