Wikipedia
SHOUTcast
SHOUTcast is cross-platform proprietary software for streaming media over the Internet. The software, developed by Nullsoft, is available free of charge. It allows digital audio content, primarily in MP3 or High-Efficiency Advanced Audio Coding format, to be broadcast to and from media player software, enabling the creation of Internet radio "stations".
The most common use of SHOUTcast is for creating or listening to Internet audio broadcasts; however, video streams exist as well. Some traditional radio stations use SHOUTcast to extend their presence onto the Web.
SHOUTcast Radio is a related website which provides a directory of SHOUTcast stations.