WordNet (r) 3.0 (2006):

critical mass
    n 1: the minimum amount (of something) required to start or
         maintain a venture; "the battle for the computer market has
         now reached critical mass"; "there is now a critical mass
         of successful women to take the lead"; "they sold the
         business because it lacked critical mass"
    2: the minimum mass of fissionable material that can sustain a
       chain reaction

The Jargon File (version 4.4.7, 29 Dec 2003):

critical mass
 n.

    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.


The Free On-line Dictionary of Computing (30 December 2018):

critical mass

   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)