Source : WordNet®

XXX
     n 1: the cardinal number that is the product of ten and three
          [syn: {thirty}, {30}]
     2: (genetics) abnormal complement of three X chromosomes in a
        female

Source : Free On-Line Dictionary of Computing

XXX
     
        /X-X-X/ A marker that attention is needed.  Commonly used in
        program comments to indicate areas that are {kluge}d or need
        to be.  Some hackers liken "XXX" to the notional heavy-porn
        movie rating.  Compare {FIXME}.
     
        [{Jargon File}]