DuckCorp Dico

Found one definition

1.                 From The Jargon File (version 4.4.7, 29 Dec 2003):
                   
   
   
                   
                     
   OT
    //
       [Usenet: common] Abbreviation for “off-topic”. This is used to respond to a
       question that is inappropriate for the newsgroup that the questioner posted
       to. Often used in an HTML-style modifier or with adverbs. See also TAN.