Podcasting started a few months ago among a small group of geeks who cobbled together some software that makes it easy to download sound files from the Web and squirt them right into an iPod or other portable music player.
The best description I've seen for it is in this article, which calls it "Tivo for radio." Podcasting allows you to download audio content and listen to it whenever you like, as opposed to listening to radio live.
In just the way Tivo has begun the deconstruction of broadcast television, podcasting will begin to change broadcast radio. Anyone with a microphone and a computer can make their own podcasts, and that is exactly what is happening. "Radio" has been freed from the confines of corporate control.
These are interesting times.