- Probability: Probability is a quantitative measure of certainty.
- Experiment: A job which produces some outcomes.
- Trial: Performing an experiment.
- Event: The group of outcomes, denoted by capital letter of English alphabets like A, B, E etc.
- The empirical (or experimental) probability P(E) of an event E is given by

- The probability of an event lies between 0 and 1 (0 and 1 are included)
- Impossible event: Event which never happen.
- Certain event: Event which definitely happen.
- The probability of sure event is 1.
- The probability of an impossible event is 0.
- The probability of an event E is a number P(E) such that 0 < P(E) < I.