In the social sciences, social stratification is any given society's categorization of its people into rankings of socioeconomic tiers based on factors like wealth, income, social status, occupation, and power. Stratification is the relative social position of persons in a given social group, category, geographical region or other social unit. In modern Western societies, stratification is often broadly divided into three main divisions of social class: upper class, middle class, and lower class. Each of these classes can be further subdivided into smaller classes (e.g., "upper-middle").

Social inequality is characterized by the existence of unequal opportunities and rewards for different social positions or statuses within a group or society. It contains structured and recurrent patterns of unequal distributions of goods, wealth, opportunities, rewards, and punishments. Racism, for example, is understood to be a phenomenon whereby access to rights and resources is unfairly distributed across racial lines. Conversely, "white privilege" is a concept developed by social scientist Peggy McIntosh to refer to the myriad ways in which white people benefit from racial inequality, in particular.
There are two main ways to measure social inequality: inequality of conditions, and inequality of opportunities. Inequality of conditions refers to the unequal distribution of income, wealth and material goods. Housing, for example, is an inequality of conditions with the homeless and those living in housing projects sitting at the bottom of the hierarchy while those living in multi-million dollar mansions sitting at the top. Another example is at the level of whole communities, where some are poor, unstable, and plagued by violence, while others are invested in by business and government such that they thrive and provide safe, secure, and happy conditions for their inhabitants.