Critical mass
WordNet
noun
(1) The minimum mass of fissionable material that can sustain a chain reaction
(2) 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"
WiktionaryText
Noun
- the amount of fissile material that is needed to support a self-sustaining nuclear chain reaction
- A quantity or amount required to trigger a phenomenon.