A podcast (or non-streamed webcast) is a series of digital media files (either audio or video) that are released episodically and often downloaded through web syndication. (Wikipedia)

While not education related, here is an example of an audio podcast from a Ricky Gervais comedy skit.  There are also examples of a video podcasts through Vodpod at the bottom of the right hand side menu.

However, more than simply uploaded audio/video files waiting to be accessed, podcasts provide users with the ability to subscribe to regular downloads:

Download podcasting software such as Juice Receiver (an Open Source cross-platform podcast receiver), Apple’s iTunes for Mac and Windows or similar podcasting software. These programs allow you to schedule regular updates to your selected downloads with an iPod or other MP3 player.