![](https://cos-cdn.shuashuati.com/pipixue-wap/2020-1230-1107-56/ti_inject-812ce.png)
It is a type of events. For example, there are A, B, C three events, and the probability of the union of A and B equals the probability of A times the probability of B, but the probability of the union of A, B and C is not necessarily equal to the probability of A times the probability of B times the probability of C.