Social stratum

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.

The categorization of people by social strata occurs in all societies, ranging from the complex, state-based or polycentric societies to tribal and feudal societies, which are based upon socio-economic relations among classes of nobility and classes of peasants. Historically, whether or not hunter-gatherer societies can be defined as socially stratified or if social stratification began with agriculture and common acts of social exchange, remains a debated matter in the social sciences. Determining the structures of social stratification arises from inequalities of status among persons, therefore, the degree of social inequality determines a person's social stratum. Generally, the greater the social complexity of a society, the more social strata exist, by way of social differentiation.

...
Wikipedia