Source : Webster's Revised Unabridged Dictionary (1913)

Masquerade \Mas`quer*ade"\, v. i. [imp. & p. p. {Masqueraded};
   p. pr. & vb. n. {Masquerading}.]
   1. To assemble in masks; to take part in a masquerade.

   2. To frolic or disport in disquise; to make a pretentious
      show of being what one is not.

            A freak took an ass in the head, and he goes into
            the woods, masquerading up and down in a lion's
            skin.                                 --L'Estrange.

Source : Free On-Line Dictionary of Computing

masquerading
     
        1.  "{NAT}" ({Linux} {kernel} name).
     
        2.  Hiding the names of internal e-mail {client}
        and {gateway} machines from the outside world by rewriting the
        "From" address and other {headers} as the message leaves the
        organisation.
     
        This is good practise because external users do not need to
        know about internal changes in message routing.  The external
        mail gateway needs to know how to route incoming replies back
        to the original sender.
     
        (1998-03-03)