RealAudio was developed by RealNetworks and supports FM-stereo-quality sound. To hear a Web page that includes a RealAudio sound file, you need a RealAudio player or plug-in, a program that is freely available from a number of places.
More information is available on RealNetwork web site.
To convert other audio formats to RealAudio, you will need River Past RealMedia Booster Pack in addition to your audio software.