● Random phenomenon: The probability of any outcome of a random phenomenon is the proportion of times the outcome would occur in a very long series of repetitions. ● Outcome: the result of an experiment ● Event: a set of outcomes in which a probability is assigned to subjects ● The law of large numbers: says that as a sample size grows, its mean gets closer to the average of the whole population. ● Independence: is when the variables don't depend on each other ● P: is often used to represent probability, if P is 0, there is no chance that event happens, and if P is 1, there is a 100% chance it will happen.