Why was American society given the label the Gilded Age in the 1880s/1890s?

The term Gilded Age actually comes from the novel written by the great Mark Twain. He used this title to indicate something marvelous, shining and glittering on the surface but corrupted from the inside. The Gilded Age was a period of great advancements and of a major economic boom but that was all fueled by big corporations with shady practices who mistreated their workers and political corruption.