The experiment consists of a sequence of independent trials.

Each trial results in one of two outcomes: success, , or failure, .

The geometric random variable is defined as the number of trials until the first is observed.

The probability is the same for each trial.

Suppose an ordinary die is thrown repeatedly until the first time a "1" appears. The probability distribution of the number of times it is thrown is supported on the infinite set { 1, 2, 3, ... } and is a geometric distribution with p = 1/6.