Interval variables are a type of quantitative variable where the difference between values is meaningful. They have a defined order and equal intervals, allowing for the measurement of the distance between values. A common example of an interval variable is temperature measured in degrees Celsius or Fahrenheit, where the difference between 20°C and 30°C is the same as between 30°C and 40°C. However, interval variables do not have a true zero point. For instance, 0°C does not mean the absence of temperature; it is simply a point on the scale. This characteristic distinguishes interval variables from ratio variables, which do have a true zero and allow for a wider range of mathematical operations.