If a value assigned to a unit is non-numerical.

In software quality engineering, data can be classified as either numerical or non-numerical.

Numerical data can be measured and expressed in numbers, such as weight, height, and temperature.

Non-numerical data, also known as categorical data, represents characteristics or attributes that cannot be measured in numbers.

Such data is described as "qualitative" because it pertains to qualities rather than quantities.

References: The ASQ (American Society for Quality) defines qualitative data as data that approximates or characterizes but does not measure attributes, properties, or characteristics of a phenomenon.