In developed nations across the world, the lower middle class is a sub-division of the greater middle class. Universally the term refers to the group of middle class households or individuals who have not attained the status of the upper middle class associated with the higher realms of the middle class, hence the name.

In American society, the middle class may be divided into two or three sub-groups. When divided into two parts, the lower middle class, also sometimes simply referred to as "middle class", consists of roughly one third of households, roughly twice as large as the upper middle or managerial class. Common occupation fields are semi-professionals, such as lower-level managers or school teachers, small business owners and skilled craftsmen. These individuals commonly have some college education or perhaps a Bachelor's degree and earn a comfortable living. Already among the largest social classes, rivaled only by the working class, the American lower middle class is diverse and growing.

The middle class is a class of people in the middle of a societal hierarchy. In Weberian socio-economic terms, the middle class is the broad group of people in contemporary society who fall socio-economically between the working class and upper class. The common measures of what constitutes middle class vary significantly between cultures.

The term "middle class" is first attested in James Bradshaw's 1745 pamphlet Scheme to prevent running Irish Wools to France. The term has had several, sometimes contradictory, meanings. It was once defined by exception as an intermediate social class between the nobility and the peasantry of Europe.^{[by whom?]} While the nobility owned the countryside, and the peasantry worked the countryside, a new bourgeoisie (literally "town-dwellers") arose around mercantile functions in the city. Another definition equated the middle class to the original meaning of capitalist: someone with so much capital that they could rival nobles. By this definition, only millionaires and billionaires are middle class in modern times. In fact, to be a capital-owning millionaire was the essential criterion of the middle class in the industrial revolution. In France, the middle classes helped drive the French Revolution.