Broadcast Research Definitions describes demographics as:
a system of categories by which a population is subdivided according to characteristics of the people who comprise it. The same term also describes audience reports which present audiences according to this system of categories. In broadcast ratings demographics most often refer to age and sex categories such as “Men 18–34” or “Women 25–49.” The terms may also be used to describe categories based on marital status, education, etc.
Demographics are important in the radio industry in two ways. First, advertisers use demographics to describe their customers and to buy audiences for commercials. This practice is the basic revenue ...