In mathematics, statistics and other areas of quantitative research and analysis, data which is neither measured, nor ordered, but just classified and put into certain categories, the scale of measurement is called a nominal scale. Without measurement, sorting or re-hashing, data is classified into fixed categories based solely on their qualitative aspects.
‘Mode’ is used as a measure of central tendency for the nominal scale of data. Mode is the most frequently occurring piece of data within a data set. Median on the other hand, does not matter for the nominal scale data, since there is no sorting or ordering.
When qualitative aspects such as caste, gender, visual pattern, nationality, biological species genre, defined styles etc are used to classify data into sub groups, we can call it use of nominal scale