On 5.1, what is the process named "idle"?

[Joe Altman]

Greetings, list subsribers...

I've installed 5.1 and a variety of apps on a machine, in preparation
for a move to 5.1 in the near future, and in the course of playing
around on it, I've noticed a process called idle:

~games: top -SU root
PID USERNAME PRI NICE SIZE RES STATE TIME  WCPU   CPU     COMMAND
11  root     -16 0    0K   12K RUN   59:26 94.48% 94.48%  idle

~games: more /usr/local/bin/idle
#!/usr/local/bin/python

from idlelib.PyShell import main
main()

What is idle? Is it showing the percentage of CPU unused, or some
similar thing? I poked around with apropos, and man, and briefly
looked around through the file tree, but saw nothing; I also note that
there is no apparent equivalent process on my 4.9 machine.

Thanks in advance for any answers,

fj