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 can never be fixed it can only be discarded and rewritten. [Jargon File] (1994-12-23)