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

channel op
 /chan'l op/, n.

    [IRC] Someone who is endowed with privileges on a particular IRC channel;
    commonly abbreviated chanop or CHOP or just op (as of 2000 these short
    forms have almost crowded out the parent usage). These privileges include
    the right to kick users, to change various status bits, and to make
    others into CHOPs.


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

channel op
chan op
CHOP

    /chan'l op/ (Or "op", "chan op", "chop") Someone
   who is endowed with privileges on a particular IRC
   channel.  These privileges include the right to kick
   users, to change various status bits and to make others into
   CHOPs.

   The full form, "channel operator", is almost never used.

   [Jargon File]

   (1998-01-08)