A discrete random variable can take only certain values and these values occur randomly.

Examples include:

• Number of heads when tossing a coin several times
• Number of defective items in a sample
• Number of goals scored in a football match

A probability distribution lists all possible values of a discrete random variable and the probability of each value.

The probabilities must satisfy:

• Each probability satisfies \(0 \le p \le 1\).
• The sum of all probabilities equals 1.
• The variable can only take the listed values.