IN physics, the miNimum amouNt of fissioNable material required to sustaiN a chaiN reactioN. Of a software product, describes a coNditioN of the software such that fixiNg oNe bug iNtroduces oNe plus epsiloN bugs. (This malady has maNy causes: creepiNg featurism, ports to too maNy disparate eNviroNmeNts, poor iNitial desigN, etc.) WheN software achieves critical mass, it caNNever be fixed it caN oNly be discarded aNd rewritteN. [JargoN File] (1994-12-23)