Podcasting is the distribution of audio or video files, such as radio programs or music videos, over the internet using RSS syndication for listening on mobile devices and personal computers. A podcast is a web feed of audio or video files placed on the Internet for anyone to subscribe to, and also the content of that feed. Podcasters' websites also may offer direct download of their files, but the subscription feed of automatically delivered new content is what distinguishes a podcast from a simple download

Podcasting's essence is about creating content (audio or video) for an audience that wants to listen when they want, where they want, and how they want.

For more information on podcasting (more than you'll ever need), take a look at this.