random experiment: is a mechanism that produces a definite outcome that cannot be predicted with certainty
sample space: associated with a random experiment is the set of all possible outcomes
event: is a subset of the sample space
An event E is said to occur on a particular trial of the experiment if the outcome observed is an element of the set E.
The probability of an outcome e in a sample space S is a number p between 0 and 1 that measures the likelihood that e will occur on a single trial of the corresponding random experiment. The value p = 0 corresponds to the outcome e being impossible and the value p = 1 corresponds to the outcome e being certain.
The probability of an event A is the sum of the probabilities of the individual outcomes of which it is composed. It is denoted P(A).