Gribble

from The Collaborative International Dictionary of English v.0.48

Gribble \Grib"ble\, n. [Cf. Prov. E. grib to bite.] (Zool.)
   A small marine isopod crustacean ({Limnoria lignorum} or
   {Limnoria terebrans}), which burrows into and rapidly
   destroys submerged timber, such as the piles of wharves, both
   in Europe and America.
   [1913 Webster]

from Jargon File (4.4.4, 14 Aug 2003)

gribble
 n.

   Random binary data rendered as unreadable text. Noise characters in a
   data stream are displayed as gribble. Dumping a binary file to the
   screen is an excellent source of gribble, and (if the bell/speaker is
   active) headaches.

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