[Tutor] Question about parameters of sys module

[JD]

Hi,

I am currently playing around with some "toys" I found on 
Useless Python. In the russianroulette.py script, I found a 
line that I couldn't understand.

It is this one:
[...]
os.system('clear')
[...]

I know what it does: it clears the screen. What made me 
uncertain is that the "clear" value is not documented in 
the sys module documentation.

As it is not a variable defined in the script, I suppose it 
is the parameter of a fonction of the sys module. Where may 
I find more information about it? And chat exactly is this 
'clear'? A variable?

I thank you in advance for your lights.