The term variable is developed very early in introductory algebra coursework. It is defined as a letter or symbol that can be replaced by any number or expression. Examples of variables would be as follows: x, t, d, y, *, or z. The most commonly used variable in algebra is x. If a person earns $8.00 for every hour worked and s/he works 5 hours, the person would earn $8 x 5 = $40. If the person works for n hours, that person would earn $8 x n or $8n.

In the application of functions, variables are used to represent the relationship between two things. The independent variable is referred to as x and the dependent variable is referred to as y. It is common to write functions in terms of the independent variable.

In probability work, a random variable is a numeric quantity that can be measured in a random experiment. It is a function of the possible outcomes of an experiment. If a baseball player is up at bat ten times, the random variable can be assigned to either hits or misses. If x represented the number of hits, the outcomes would be 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, or 0.