What does the term 'proletariat' refer to in Marxist theory?

In Marxist theory, the term 'proletariat' specifically refers to the working class, which is composed of individuals who do not own the means of production and must sell their labor to survive. Karl Marx emphasized the crucial role of the proletariat in the capitalist system, highlighting their exploitation and the relationship to the bourgeoisie, or the capitalist class, which owns the means of production. The proletariat is seen as a vital force for revolutionary change, as Marx believed that their struggles could lead to a class consciousness that would ultimately overthrow the capitalist system.

In this context, the other choices do not align with the definition of the proletariat. The ruling class, described in the first option, refers to the bourgeoisie, whereas the upper middle class corresponds more to a socio-economic group within capitalism but is not synonymous with the proletariat. The agricultural class, mentioned in the last option, typically pertains to those engaged in farming and may include both landowners and laborers, but it does not encapsulate the broader working class defined by Marx. Thus, the correct interpretation of 'proletariat' within Marxist theory is the working class.