What is podcasting?
A podcast is a series of digital media files, usually digital audio or video, that is made available for download via Web syndication. The syndication aspect of the delivery is what differentiates podcasts from other files accessible by direct download or streaming: it means that special software applications, generically known as podcatchers (such as Apple's iTunes or Nullsoft's Winamp), can automatically identify and retrieve new files associated with the podcast when they are made available, and that these files can be stored locally on the user's computer or other device for offline use. This is done by the podcatcher accessing a centrally-maintained Web feed, which lists files associated with a certain podcast.

For help for podcasting on iTunes follow this link