A Podcast is an mp3 sound file which is shared on the internet; it can also be ordered as an RSS feed or an Atom feed to your own computer or your mp3 player, and can be listened to whenever it suits you. The term 'podcasting' on the other hand refers to making the podcasts, and sharing or distributing them. They can be listened to with any media player or portable player.
With podcasts you can easily reach huge audiences on the internet. Podcasts are available on almost every subject possible. Also scientific journals have on their homepages podcasting files related to current events in their discipline. For example, the journal Nature has a podcast service where they release a weekly mp3 file of news and interviews from the latest issue.
You can order podcasts of presentations from conference home pages.
Files can be downloaded directly in mp3 format from websites. You should note that if you do this, you can only download the most recent file, and not for example all the episodes of a program or updates to a file.
RSS or Atom feeds
With a feed you can order sound files to download automatically according to how often it is updated.
In order to receive podcasts, there are several different free programs like Juice or iTunes. Feed readers or programs check at certain intervals whether the requested feed has been updated. They have the ability to download a new file automatically and inform the user about it.