In general terms, it can be called 'broadcast monitoring and reporting'. Any broadcast content can be digitally encoded - or 'watermarked' - so that airplay can be monitored, reported or confirmed. A variety of other names are also used, including broadcast data system, radio airplay monitoring, radio airplay verification, airplay information system, etc., etc.

-> "Nielsen Broadcast Data Systems (BDS), a division of Nielsen Entertainment, has been providing radio airplay data to record companies since 1989 and is regarded as the standard music monitoring service utilized by the music industry. ... In addition, Billboard and Billboard's Airplay Monitor magazines use Nielsen BDS data in the determination of their airplay charts."
http://www.xmradio.com/newsroom/screen/pr_2003_06_24.html

-> "Verance Corporation, the leading provider of tools and services to track, manage and enhance the use of media content globally, today announced that its broadcast monitoring and reporting service, ConfirMedia®, has been selected by the Ad Council for the monitoring of radio advertising campaigns nationwide. ... ConfirMedia is a broadcast and cable airplay information service employing Verance's proprietary audio watermarking technology to monitor and report the airplay of encoded commercials, music compositions, and programs on all major television and radio stations"
http://www.verance.com/news/releases/09-03-02.html

-> "Airplay Tracking Made Simple - The World's Largest Airplay Monitoring And Information Service - RadioWave is the first and only airplay monitoring system designed specifically for radio stations streaming over the Internet, and is the leading information provider on music played over streaming broadcasts."
http://www.radiowavemonitor.com/about.html