gray goo

gray goo n.  A hypothetical substance composed of
   {sagan}s of sub-micron-sized self-replicating robots programmed
   to make copies of themselves out of whatever is available.  The
   image that goes with the term is one of the entire biosphere of
   Earth being eventually converted to robot goo.  This is the
   simplest of the {{nanotechnology}} disaster scenarios, easily
   refuted by arguments from energy requirements and elemental
   abundances.  Compare {blue goo}.