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 x,y or z, used to represent an unspecified number of a specific type; for example, the variable x could represent an unspecified real number.