variable

a numerical property that can have more than one value.

An example of a variable is age in years. This is a property of every person, and it can have any value from 0 to over 120. Because it can vary from measurement to measurement, age is a variable. Variables can have different types of scale: nominal, ordinal, interval, and ratio.

There are two kinds of numerical properties: variables and constants. Constants always have the same value (for example, the number of hours in a day is always 24). Constants are constant, as the name implies: like the number of hours in a day, they do not vary.