The term Gilded Age was first coined by Mark Twain and Charles Dudley Warner in their book The Gilded Age: A Tale of Today. Gilding refers to the practice of putting small amounts of precious metals over the top of a larger, less precious material. The insinuation was that although America was in the middle of a period of great national wealth, this was all a façade, or gilding over, of serious social problems which affected the larger part of the population.
During the 1870’s and 1880’s, America experienced its largest period of economic growth in its history. Almost every measure of economic health increased substantially. GDP went way up, farm output nearly doubled, mileage of railroad multiplied by a factor of 5 while coal production multiplied by a factor of 8. Entire cities sprung up in the northeast as the industrial capacity of our country hit overdrive. By the end of the decade, per capita income in the U.S. was the highest in the world, and nearly 50% more than any other country. Names like Carnegie, Morgan, Aster and Vanderbilt became internationally known as these industrialists and captains of industry amassed huge fortunes.
But under this great acquisition of wealth were severe social issues. Much of the countries wealth was acquired through cutthroat business tactics and horrific workplace policies. Child labor and extended hours were commonplace, to say nothing of deplorable workers housing, widespread malnutrition and disgusting sanitation. Labor movements were just starting to affect these problems, but we were still years away from anything resembling workmans comp, safety inspections or even mandatory fire codes. This problem was compounded by a rise in the rate of urbanization and large waves of immigration. Widespread racism and violent resistant was common as native born citizens competed with immigrants and newly freed slaves for low paying industrial or agricultural jobs.
As you can see, Gilded is the perfect metaphorical term for this period.