The sample size needed to generate meaningful results is greater than for parametric data and tests. NonParametric data types are called Nominal or Ordinal. Interpretation can be derived from examining mean and variance. These tests assume an independent selection of subjects, also that variances among data elements are equal or at least known. Parametric data types are called Interval or Ratio.
Nominal data identify subjects by category or by name.
These data simply count frequencies of occurrence. The numbers may represent categories, or serve to distinguish groups. The numbers do not reflect differences in magnitude or quantity. Some examples may include identifying subjects' Gender, Ethnicity, Class, HairColor, and the like. You would not use an arithmetic Mean to describe the groups.