In Marxist theory, the Lumpenproletariat is the underclass devoid of class consciousness. Karl Marx and Friedrich Engels coined the word in the 1840s and used it to refer to the unthinking lower strata of society exploited by reactionary and counter-revolutionary forces, particularly in the context of the revolutions of 1848. They dismissed the revolutionary potential of the Lumpenproletariat and contrasted it with the proletariat. Among other groups, criminals, vagabonds, and prostitutes are usually included in this category.

The proletariat is the social class of wage-earners, those members of a society whose only possession of significant economic value is their labour power. A member of such a class is a proletarian or a proletaire. Marxist philosophy regards the proletariat under conditions of capitalism as an exploited class⁠—  forced to accept meager wages in return for operating the means of production, which belong to the class of business owners, the bourgeoisie.