Level of measurement

https://en.wikipedia.org/wiki/Level_of_measurement

Level of measurement or scale of measure is a classification that describes the nature of information within the values assigned to variables.

Psychologist Stanley Smith Stevens developed the best-known classification with 4 levels (or scales) of measurement: nominal, ordinal, interval, and ratio.

Stevens claimed that all measurement in science was conducted using 4 different types of scales that he named nominal, ordinal, interval and ratio, unifying both qualitative (which are described by his nominal type) and quantitative (to a different degree, described by his other scales). The concept of scale types later received the mathematical rigour that it lacked at its inception.