A nominal category (also nominal variable or nominal group) is a collection of objects or ideas grouped according to a particular qualitative property. Nominal categories do not have a natural order, which means that statistical analyses of these variables will always produce the same results, regardless of the order in which the data is presented.
A variable used to associate each data point in a set of observations, or in a particular instance, to a certain qualitative category is a categorical variable. Categorical variables have two types of scales, ordinal and nominal. The first type of categorical scale is dependent on natural ordering, levels that are defined by a sense of quality. Variables with this ordering convention are known as ordinal variables. In comparison, variables with unordered scales are nominal variables.