Short answers, pulled from the story.
Social class, also called a social stratum, is a grouping of people into hierarchical social categories, most commonly the working class, the middle class, and the upper class. Membership is commonly considered dependent on education, wealth, occupation, income, and belonging to a particular subculture or social network.
Karl Marx defined class by a person's relationship to the means of production. In modern capitalist society he saw the proletariat as those who work but do not own the means of production, and the bourgeoisie as those who invest and live off the surplus the proletariat generates and do not work at all.
Max Weber formulated a three-component theory of stratification built from class, status, and power, and refused to treat ownership of capital as the supreme factor. He noted that some aristocrats held political power without economic wealth, and that managers control firms they do not own.
The three-level economic class model divides society into an upper class that owns and controls the means of production, a middle class of professional workers, small business owners, and low-level managers, and a lower class who rely on low-paying jobs and experience poverty. The upper class is generally contained within the richest one or two percent of the population.
The Great British Class Survey was a study by BBC Lab UK, developed with academic experts, whose results were published online on the 2nd of April 2013 and slated for the journal Sociology. It surveyed 160,000 residents of the United Kingdom, measuring economic, cultural, and social capital using a framework from Pierre Bourdieu, who first published his theory of social distinction in 1979.
Societies with large class differences have a greater proportion of people who suffer anxiety and depression symptoms, and lower-class families have higher rates of infant mortality, cancer, and cardiovascular disease. Between two Stockholm suburbs, life expectancy differs by 18 years between poorer inhabitants near the station and more affluent inhabitants near Danderyd.
A class system dates back to Ancient Egypt, where elite standing was marked by literacy and the wealthy sat at the top while common people and slaves sat at the bottom. The system was not rigid, as a man of humble origins could ascend to a high post, and scribes and officials formed the upper class known as the white kilt class.