The Swing ERA was a period of time in the 1930s and 1940s when big band swing music was popular. It was characterized by large jazz bands with brass and reed instruments, as well as string sections and vocalists. The Swing ERA was a time of great innovation in jazz music, and it is often considered to be the golden age of jazz. The term 'The Swing ERA' is often abbreviated to 'ERA, ' which is the three-letter answer to this crossword puzzle.