What's with "long running processes" ?

[walterbyrd]

I understand that Python has them, but PHP doesn't.

I think that is because mod_php is built into apache, but mod_python
is not usually in apache. If  mod_python was built into apache, would
python still have long running processes (LRP)?

Do LRPs have to do with a Python interpreter running all the time? Or
is it something else?

I also understand that LRPs are the reason that shared hosting is less
common, and more expensive for python than php. The LRP have a major
effect on how many users can packed onto a single server.

As to LRPs: does it matter if you're using mod_python, fastcgi, wsgi,
scgi, cgi, or whatever?

Obviously, I am a little foggy about LRPs, can somebody help me out?