AFAIK there can only be **one** sitecustomize.py. I think the docs
should be able to have a term for the thing which contains/provides this file.

The current vacuum gets filled with a lot of different terms meaning the same
thing. This does not hurt, but still I **feel** it would help to have an
agreement on a term.

The closest we get is the PyPA/distutils-sig consensus that software
is developed by and as projects (covering libraries, applications, and
assorted other endeavours):
https://packaging.python.org/en/latest/glossary/#term-project

Thank you Nick, for providing this link. I hope your are not the author
of this text. This is no definition according to my point of view.
I read it, and don't get it.

Example: I think "django" is a
project according to this definition.

The install_requires vs requirements.txt question is covered as its
own topic, without introducing any particular terminology:
https://packaging.python.org/en/latest/requirements/

It is hard to cover the meaning of requirements.txt if there
is no common term to name the container which contains it :-)