Podcasting is an RSS-syndicated technology. Podcasts of the traditional audio sort are MP3 files. Garrison Keeler has one:
Such podcasts can be played on any computer linked to the 'net and containing the free iTunes software. iTunes searches for updates on RSS feeds every time you connect to the net (or less often if you choose).
iTunes U provides many higher education materials online. Many universities use iTunes U to disseminate materials to both students enrolled at the university (behind password) and to the public at large: http://itunesu.pbwiki.com/