Nielsen ratings are audience measurement systems developed by Nielsen Media Research, in an effort to determine the audience size and composition of television programming in the United States. Nielsen Media Research was founded by Arthur Nielsen, who was a market analyst whose career had begun in the 1920s with brand advertising analysis and expanded into radio market analysis during the 1930s, culminating in Nielsen ratings of radio programming, which was meant to provide statistics as to the markets of radio shows. In 1950, Nielsen moved to television, developing a ratings system using the methods he and his company had developed for radio. That method has since become the primary source of audience measurement information in the television industry around the world. - Source: Wikipedia
