gray goo

n. A hypothetical substance composed of sagans 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.
