The document discusses the evolution and decline of CD sales over time. It notes that CDs gained popularity in the 1980s and 1990s as a means of storing and playing audio, but that sales have declined in recent years as music has become more freely accessible online. This has caused a major drop in CD sales. However, the document explains that artists still make money through merchandise sales at concerts and licensing their music for movies and TV, bringing in hundreds of thousands of dollars through these alternative revenue streams.