Source : Free On-Line Dictionary of Computing

retcon
     
        /ret'kon/ retroactive continuity.
     
        The common situation in fiction where a new story "reveals"
        things about events in previous stories, usually leaving the
        "facts" the same (thus preserving continuity) while completely
        changing their interpretation.  For example, revealing that a
        whole season of "Dallas" was a dream was a retcon.
     
        This term was once thought to have originated on the {Usenet}
        newsgroup {news:rec.arts.comics} but is now believed to have
        been used earlier in comic fandom.
     
        [{Jargon File}]
     
        (1994-12-08)