The Free On-line Dictionary of Computing (30 December 2018):

network address
network number

    1. The network portion of an IP address.  For a
   class A network, the network address is the first byte of
   the IP address.  For a class B network, the network address
   is the first two bytes of the IP address.  For a class C
   network, the network address is the first three bytes of the
   IP address.  In each case, the remainder is the host
   address.  In the Internet, assigned network addresses are
   globally unique.

   See also subnet address, Internet Registry.

   2. (Or "net address") An electronic mail address on the
   network.  In the 1980s this might have been a bang path but
   now (1997) it is nearly always a domain address.  Such an
   address is essential if one wants to be to be taken seriously
   by hackers; in particular, persons or organisations that
   claim to understand, work with, sell to, or recruit from among
   hackers but *don't* display net addresses are quietly presumed
   to be clueless poseurs and mentally flushed.

   Hackers often put their net addresses on their business cards
   and wear them prominently in contexts where they expect to
   meet other hackers face-to-face (e.g. science-fiction
   fandom).  This is mostly functional, but is also a signal
   that one identifies with hackerdom (like lodge pins among
   Masons or tie-dyed T-shirts among Grateful Dead fans).  Net
   addresses are often used in e-mail text as a more concise
   substitute for personal names; indeed, hackers may come to
   know each other quite well by network names without ever
   learning each others' real monikers.

   See also sitename, domainist.

   [Jargon File]

   (1997-05-10)