A combination of the words "iPod" and "broadcast," is a collection of digital media files which is distributed over the Internet, often using syndication feeds, for playback on portable media players (mp3 players, iPods, Zunes, etc) and personal computers. The term podcast, like "radio," can refer either to the content itself or to the method by which it is syndicated (from http://en.wikipedia.org/wiki/Podcast, retrieved March 3, 2008). Creating and downloading podcasts is free of charge..

Or more simply, it is an audio or video recording that you can listen to on your computer or transfer to a portable mp3 device. Often you can subscribe (for free!) to a podcast which will automatically notify you each time they release a new "episode."

Podcast episode: term sometimes used to describe individual podcasts in a series.

Syndication feed/format: A publishing format that lets people view headlines of the latest updates from their favorite blogs and Web sites all from within a single newsreader program. The major syndication formats are RSS and Atom, and most newsreaders support both formats. More on the TechWeb Enyclopedia

Listing of software options, tutorials, examples, and other resources!
http://teachdigital.pbwiki.com/podcasting