An interval scale is a type of measurement scale that not only categorizes data but also allows for the measurement of the difference between values. It has equal intervals between points, meaning the difference between any two values is meaningful. A common example of an interval scale is the Celsius temperature scale, where the difference between 10°C and 20°C is the same as between 20°C and 30°C. However, an interval scale does not have a true zero point, which means that zero does not indicate the absence of the quantity being measured. For instance, in the Celsius scale, 0°C does not mean there is no temperature; it simply represents a specific point on the scale.