What is a Podcast?

Short Answer

Think of a podcast as a radio show downloaded to your ipod/mp3 player that you can listen to whenever you choose. itunes as well as other software can be used to automatically update the most current show of your favorite podcasts (from the web to your mp3 player) so that you always have the newest content on you mp3 player.

Long Answer

There is no way that I am going to be able to give a better explanation than the Wikipedia article on podcasting.