Social stratification refers to a society's categorization of its people into groups based on socioeconomic factors like wealth, income, race, education, ethnicity, gender, occupation, social status, or derived power (social and political). It is a hierarchy within groups that ascribe them to different levels of privileges. As such, stratification is the relative social position of persons within a social group, category, geographic region, or social unit.
In modern Western societies, social stratification is defined in terms of three social classes: an upper class, a middle class, and a lower class; in turn, each class can be subdivided into an upper-stratum, a middle-stratum, and a lower stratum. Moreover, a social stratum can be formed upon the bases of kinship, clan, tribe, or caste, or all four.