The Free On-line Dictionary of Computing (19 January 2023):

op

    /op/ 1. In England and Ireland, a common verbal
   abbreviation for "operator", as in system operator.  This is
   less common in the US, where sysop seems to be preferred.

   2. The general term for an IRC channel op.  Also, as a
   verb: to give someone channel op privileges.  Compare
   ircop.

   [Jargon File]

   (1997-12-12)


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

OP
 //

    [Usenet; common] Abbreviation for “original poster”, the originator of a
    particular thread.


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

op
 /op/, n.

    1. In England and Ireland, common verbal abbreviation for ‘operator’, as in
    system operator. Less common in the U.S., where sysop seems to be
    preferred.

    2. [IRC] Someone who is endowed with privileges on IRC, not limited to a
    particular channel. These are generally people who are in charge of the IRC
    server at their particular site. Sometimes used interchangeably with CHOP
    . Compare sysop.