The Jargon File (version 4.4.7, 29 Dec 2003):

netlag
 n.

    [IRC, MUD] A condition that occurs when the delays in the IRC network or
    on a MUD become severe enough that servers briefly lose and then
    reestablish contact, causing messages to be delivered in bursts, often with
    delays of up to a minute. (Note that this term has nothing to do with
    mainstream ?jet lag?, a condition which hackers tend not to be much
    bothered by.) Often shortened to just ?lag?.


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

netlag
lag

    A condition that occurs when the delays in the
   IRC network, a MUD connection, a telnet connection, or
   any other networked interactive system, become severe enough
   that servers briefly lose and then reestablish contact,
   causing messages to be delivered in bursts, often with delays
   of up to a minute.  (Note that this term has nothing to do
   with mainstream "jet lag").

   [Jargon File]

   (1996-06-21)