(1) inevitable event: the event that will happen under condition S is called the inevitable event relative to condition S;

(2) Impossible events: events that will not happen under condition S are called impossible events relative to condition S;

(3) Deterministic events: inevitable events and impossible events are collectively referred to as deterministic events relative to condition S;

(4) Random events: events that may or may not occur under condition S are called random events relative to condition S;

(5) Frequency and frequency: repeat the test for n times under the same condition S, and observe whether there is an event A, saying that the frequency of the event A is the frequency of the event A; The ratio fn(A) of event A = the probability of event A: for a given random event A, if the frequency fn (a) of event A is stable at a certain constant with the increase of test times, the constant is recorded as P(A) and called as the probability of event A. ..

(6) Difference and connection between frequency and probability: The frequency of a random event refers to the ratio of the number of times nA of the event to the total number of times n of testing, which has certain stability and always swings around a certain constant, and with the increase of testing times, the swing amplitude becomes smaller and smaller. We call this constant the probability of random events, which quantitatively reflects the probability of random events. Frequency can be approximated as the probability of the event under the premise of a large number of repeated experiments.