In Marxist theory and socialist literature, the term working class is often used interchangeably with the term proletariat, and includes all workers who expend both physical and mental labour (salaried knowledge workers and white-collar workers) to produce economic value for the owners of the means of production (the bourgeoisie in Marxist literature).
As with many terms describing social class, working class is defined and used in many different ways. The most general definition, used by Marxists and socialists, is that the working class includes all those who have nothing to sell but their labor-power and skills. In that sense it includes both white and blue-collar workers, manual and mental workers of all types, excluding only individuals who derive their income from business ownership and the labor of others.
When used non-academically in the United States, however, it often refers to a section of society dependent on physical labor, especially when compensated with an hourly wage. For certain types of science, as well as less scientific or journalistic political analysis, for example, the working class is loosely defined as those without college degrees. Working-class occupations are then categorized into four groups: Unskilled laborers, artisans, outworkers, and factory workers.
A common alternative, sometimes used in sociology, is to define class by income levels. When this approach is used, the working class can be contrasted with a so-called middle class on the basis of differential terms of access to economic resources, education, cultural interests, and other goods and services. The cut-off between working class and middle class here might mean the line where a population has discretionary income, rather than simply sustenance (for example, on fashion versus merely nutrition and shelter).
Some researchers have suggested that working-class status should be defined subjectively as self-identification with the working-class group. This subjective approach allows people, rather than researchers, to define their own social class.