In statistics, a *variable* is something measurable or observable that is expected to either change over time or between individual observations. Examples of variables in statistics include the age of students, their hair colour or a playing field’s length or its shape.

*Numerical variables* are variables whose values are numbers, and for which arithmetic processes such as adding and subtracting, or calculating an average, make sense.

Examples include the number of children in a family or the number of days in a month.

A *discrete numerical variable* is a *numerical variable*, each of whose possible values is separated from the next by a definite ‘gap’. The most common numerical variables have the counting numbers 0,1,2,3,… as possible values. Others are prices, measured in dollars and cents.

In algebra, a *variable* is a symbol, such as *real number*.