nobody UNIX userid

[Tom Corsetti]

Hi!
I have seen the nobody account (user number = -2) in just about 
every passwd file that I can remember.  I have never asked myself
what purpose this account serves.  Since I always say it, I just
came to accept its presence, til now.  A minute ago, I got email
from a novice UNIX person asking me what purpose it serves.  Needless
to say, I was at a loss for words.  Can someone out there explain
the function of the nobody account?  Thanx in advance!
                                         - Tom