A radio advertisement is air time or 'slot' a radio station allows businesses to buy and promote their product or service. This forms 97% of the money that most radio stations make. Even though radio had been around since the early 1900's, radio stations didn't start broadcasting continually until the 1920's. KDKH was the first radio station in the world to have an advertisement on air that was paid for. From this moment on radio would never be the same.
