The working class (also labouring class, proletariat, or laboring class) is the class of people employed for wages, especially in manual or industrial work. Working-class jobs include blue-collar jobs, but also include moderate amounts of white-collar and service work. The working class relies on earnings from wage labour, thereby including a large majority of the population in industrialized economies, of the urban areas of non-industrialized economies, and also a significant number of the rural workforce worldwide. In Marxist theory and socialist literature, working class is often used synonymously with the term proletariat, and includes all those who expend either mental or physical labor to produce economic value for those who own the means of production. It thus includes knowledge workers and white-collar workers who work for a salary. Since wages can be very low, and since the state of unemployment is by definition a lack of independent means of income generation and a lack of waged employment, the working class also includes the extremely poor and unemployed, which are sometimes called the lumpenproletariat.