[IRC] What is 'umode'?

[Detlef Lechner]

Hi,
http://freenode.net/using_the_network.shtml: "+w (see wallops): This 
umode lets you see the wallops announcement system: Important network 
messages will be sent out via global notices; this is only for 
noncritical announcements and comments which may be of interest."
What standard or document does define 'umode' in IRC?
Does 'umode' stand for 'IRC user mode'? What does 'IRC user mode' mean 
precisely?

Regards,
Detlef Lechner