Source : Free On-Line Dictionary of Computing

line noise
     
         1. Spurious characters due to electrical
        {noise} in a communications link, especially an {EIA-232}
        serial connection.  Line noise may be induced by poor
        connections, interference or {crosstalk} from other circuits,
        electrical storms, {cosmic rays}, or (notionally) birds
        crapping on the phone wires.
     
        2. Any chunk of data in a file or elsewhere that looks like
        the results of electrical line noise.
     
        3. Text that is theoretically a readable text or program
        source but employs {syntax} so bizarre that it looks like line
        noise.  Yes, there are languages this ugly.  The canonical
        example is {TECO}, whose input syntax is often said to be
        indistinguishable from line noise.  Other non-{WYSIWYG}
        editors, such as {Multics} "{qed}" and {Unix} "{ed}", in the
        hands of a real hacker, also qualify easily, as do
        deliberately {obfuscate}d languages such as {INTERCAL}.
     
        [{Jargon File}]
     
        (1994-12-22)