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

EOU
 /E?O?U/, n.

    The mnemonic of a mythical ASCII control character (End Of User) that would
    make an ASR-33 Teletype explode on receipt. This construction parodies the
    numerous obscure delimiter and control characters left in ASCII from the
    days when it was associated more with wire-service teletypes than computers
    (e.g., FS, GS, RS, US, EM, SUB, ETX, and esp. EOT). It is worth remembering
    that ASR-33s were big, noisy mechanical beasts with a lot of clattering
    parts; the notion that one might explode was nowhere near as ridiculous as
    it might seem to someone sitting in front of a tube or flatscreen today.


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

EOU

    The mnemonic of a mythical ASCII control
   character (End Of User) that would make an ASR-33 Teletype
   explode on receipt.  This construction parodies the numerous
   obscure delimiter and control characters left in ASCII from
   the days when it was associated more with wire-service
   teletypes than computers (e.g. FS, GS, RS, US, EM,
   SUB, ETX, and especially EOT).  It is worth remembering
   that ASR-33s were big, noisy mechanical beasts with a lot of
   clattering parts; the notion that one might explode was
   nowhere near as ridiculous as it might seem to someone sitting
   in front of a tube or flatscreen today.

   [Jargon File]

   (1996-06-29)