Common knowledge is: "I know something, you know it, you know that I know it, I know that you know it, I know that you know that I know it, etc., etc. etc.: an infinite sequence.

共同知识是指,我知道一件事,你也知道这件事,你知道我知道这件事,我也知道你知道这件事,我知道你知道我知道这件事,以此类推,一个无限的循环

耶鲁公开课 - 博弈论课程节选