Categorical data are data with a limited number of unique values, which can be textual or numerical (nominal, ordinal, binary, count variables) that determine the fact of belonging to certain category. They are usually associated with uncountable signs, such as the names of goods or services, people's names, outcomes of events, gender, countries of residence.
Categorical variables are especially frequent in the surveys, since they naturally reflect the character of the person's thinking on the "agree - not agree" scale. For example, the measurement of political views and social attitudes can be carried out on the following scale: "totally disagree", "rather disagree", "difficult to answer", "rather agree", "totally agree".
Analysis of such variables takes a special place in statistics, since standard statistical procedures such as linear regression cannot be applied to categorical variables.