The word probability literally denotes 'chance', and the theory of probability deals with laws governing the chances of occurrences of phenomena which are unpredictable in nature.

Although historically the probability theory originated from the games of chance played by tossing coins, throwing dice, drawing cards, etc., its importance has enormously increased in recent years. Today, the notions of probability find important applications in almost all disciplines – physics, chemistry, biology, psychology, education, economics, business, industry, engineering, etc. The concept of probability plays a vital role in statistics.

Random experiment, outcome and event are three important concepts prevalently used in probability.

Random experiment: Random experiments are those experiments whose results depend on chance (The word 'random' may be taken as equivalent to 'depending on chance'), such as tossing a coin (or several coins).

Outcome: The result of a random experiment will be called an outcome. The possible outcomes of a random experiment may often be described in several ways, for example, in the random experiment of tossing a coin, there are 2 possible outcomes – 'Head' and 'Tail'.

Event: In the theory of probability, the term 'event' is used to denote any phenomenon which occurs in a random experiment. In effect, one or more outcomes are said to constitute an 'event'. Events may be 'elementary' or 'composite'. An event is said to be elementary, if it cannot be decomposed into simpler events. A composite event is an aggregate of several elementary events.

Although historically the probability theory originated from the games of chance played by tossing coins, throwing dice, drawing cards, etc., its importance has enormously increased in recent years. Today, the notions of probability find important applications in almost all disciplines – physics, chemistry, biology, psychology, education, economics, business, industry, engineering, etc. The concept of probability plays a vital role in statistics.

Random experiment, outcome and event are three important concepts prevalently used in probability.

Random experiment: Random experiments are those experiments whose results depend on chance (The word 'random' may be taken as equivalent to 'depending on chance'), such as tossing a coin (or several coins).

Outcome: The result of a random experiment will be called an outcome. The possible outcomes of a random experiment may often be described in several ways, for example, in the random experiment of tossing a coin, there are 2 possible outcomes – 'Head' and 'Tail'.

Event: In the theory of probability, the term 'event' is used to denote any phenomenon which occurs in a random experiment. In effect, one or more outcomes are said to constitute an 'event'. Events may be 'elementary' or 'composite'. An event is said to be elementary, if it cannot be decomposed into simpler events. A composite event is an aggregate of several elementary events.