Putting on the Ritz is an idiom that means to dress or act in a very fancy and luxurious manner. It is derived from the popular 1929 song of the same name, written by Irving Berlin. The song was popularized by Fred Astaire in the 1933 movie musical 'Puttin' on the Ritz'. The phrase has become a part of popular culture and is often used to describe someone who is trying to impress others with their wealth and style.