Short answers, pulled from the story.
The term middle class first appeared in print in 1745 within a pamphlet titled Scheme to prevent running Irish Wools to France written by James Bradshaw. This document focused on trade regulations and the movement of wool from Ireland to France rather than modern economics. The concept described a specific group of people existing between the nobility and the peasantry in late-feudal society.
Barbara Ehrenreich and John Ehrenreich defined the professional-managerial class in 1977 as salaried mental workers who do not own the means of production. This group includes academics, teachers, social workers, engineers, accountants, managers, nurses, and middle-level administrators. Their definition distinguishes this class by their training and education which typically includes business qualifications and university degrees.
According to the Center for Strategic and International Studies, 420 million people or 31% of the Chinese population qualified as middle class by 2013. The World Bank definition of middle class as those having daily spending between $10 and $50 per day indicated that nearly 40% of the Chinese population were considered middle class as of 2017. This growth occurred when the Chinese middle class expanded from 15% to 62% of the population between 1990 and 2005.
The OECD defines the middle class as households with income between 75% and 200% of the median national income. A 2010 working paper by the OECD asserted that 1.8 billion people were members of the global middle class. Credit Suisse's Global Wealth Report 2014 released in October 2014 estimated that one billion adults belonged to the middle class with wealth ranging from $10,000 to $100,000.
A 2014 study by Standard Bank economist Simon Freemantle found that 15.3 million households in 11 surveyed nations of Africa are middle class. A 2014 study by the German Development Institute reported that the middle class of Sub-Saharan Africa rose from 14 million to 31 million people between 1990 and 2010. In South Africa, a report by the Institute for Race Relations in 2015 estimated that between 10% and 20% of South Africans are middle class.