A plague of bionano (non-drexlerian) goo; especially of strong biotic form. Green Goo outbreaks are (like Golden Goo) quite common, but easily managed, at least in those areas with good access to blue goo and equivalent.
 Facetious term for biological life spreading throughout the galaxy. c.f. pink goo.
 (archaic) The scenario of nanomachines or bio-engineered organisms used for human population control, either by governments or eco-terrorist groups (generally by sterilizing people through otherwise harmless infections).