A podcast is a digital media file, or a collection of such files which constitute a program or in this case sermons. A Podcast is an audio or video file which is distributed over the Internet using syndication feeds for playback on mp3 players or a portable video player such as the Video capable ipods or through personal computers. A podcast is distinguished from other digital media formats by its ability to be syndicated,  and subscribed to, and downloaded automatically when new content is added, using an aggregator program such as itunes. When your audio device is synced to your computer the new podcasts that you subscribe to are loaded into the device and the episodes you have listened to are removed.