Definition of critical mass noun from the Oxford Advanced Learner's Dictionary

     

    critical mass

     noun
    noun
    BrE
     
    ; NAmE
     
    [uncountable, singular]
     
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  1. 1(physics) the smallest amount of a substance that is needed for a nuclear chain reaction to take place
  2. 2the minimum amount of resources, number of customers, etc. needed to start or support a project or an activity, or the minimum size that a project or activity needs to be in order to be successful The company needs one million customers to reach critical mass and start making a profit. TV via Internet could only be developed once a critical mass of households had broadband access.
See the Oxford Advanced American Dictionary entry: critical mass