GLASS in "The Samba Team announces Samba 3.0.0 beta3"

The Samba web site contains "The Samba Team announces Samba 3.0.0 
beta3".  This document includes a section titled "Trust Relationships 
and a Samba Domain".  I was confused by the following lines in that 
section:

"2) connect the trust from the Samba domain using
      'net rpc trustdom establish GLASS'

To create a trustlationship[sic] with SAMBA as the trusted domain:

   1) create the initial trust account for GLASS using
      'smbpasswd -a -i GLASS'.  You may need to create a UNIX
      account for GLASS$ prior to this step (depending on your
      local configuration)."

What does "GLASS" represent?