Social stratification is a society's categorization of people into socioeconomic strata, based upon their occupation and income, wealth and social status, or derived power (social and political). 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 typically is distinguished as three social classes: (i) the upper class, (ii) the middle class, and (iii) the lower class; in turn, each class can be subdivided into strata, e.g. the upper-stratum, the middle-stratum, and the lower stratum. Moreover, a social stratum can be formed upon the bases of kinship or caste, or both.