(physics物理)the smallest amount of a substance that is needed for a nuclear chain reaction to take place（核链式反应的）临界质量
the 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（启动或支持项目或活动所需的）最小资源量，最低人数；（项目或活动成功所需的）最小规模
The company needs one million customers to reach critical mass and start making a profit.公司需要 100 万客户才能达到临界规模并开始赢利。
TV via internet could only be developed once a critical mass of households had broadband access.在足够多的家庭拥有宽带接入时，网络电视才能开发。