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

Inizia leggendo il User Guide, in particolare il glossario e i tutorial che trattano l’installazione e il packaging, quindi confronta le indicazioni per librerie e applicazioni descritte nell’issue. Chiarisci la distinzione e indica quali indicazioni si applicano a ciascun tipo di progetto, tenendo conto dell’issue correlata sulla terminologia di progetto più ampia. Il lavoro è completato quando il User Guide comunica coerentemente questi casi d’uso.