Under the same conditions, n tests were carried out. In these n tests, the frequency n(A) of event A is called the frequency of event A. The ratio of nA/n is called the frequency of event A..

When the number of repeated experiments n increases gradually, the frequency fn(A) shows stability and gradually stabilizes at a constant, which is the probability of event A.

For example, if I flip a coin five times and the heads appear twice, the frequency is 2/5.

But it can't be said that the probability is 2/5.

When I throw the frequency countless times, the probability is equal to 1/2.