A podcast is much like an audio magazine subscription: a subscriber receives regular audio programs delivered via the internet, and she or he can listen to them at her or his leisure.

Podcasts differ from traditional internet audio in two important ways. In the past, listeners have had to either tune in to web radio on a schedule, or they have had to actively download individual files from webpages. Podcasts are more flexible and much easier to get. They can be listened to at any time because a copy is on the listener's computer or portable music player, and they are automatically delivered to subscribers, so no active downloading is required.

Overview
The ipodder.org definition written by Dave Winer: "Think how a desktop aggregator works. You subscribe to a set of feeds, and then can easily view the new stuff from all of the feeds together, or each feed separately. Podcasting works the same way, with one exception. Instead of reading the new content on a computer screen, you listen to the new content on any capable mp3 player on the computer or hardware player such as the iPod. Think of your player with podcasting as having a set of subscriptions that are checked regularly for updates. "

History
Podcasting was developed thanks to Adam Curry's original iPodder script and the success it fostered since August, 2004.

The first documented use of the term podcasting can be cited in an article by Ben Hammersley in an article for The Guardian in February 2004. It was perhaps first used in this context by Dannie J. Gregoire on September 15, 2004, who also registered the domain name podcasting.net. That usage was discovered and reported on by Dave Slusher of the Evil Genius Chronicles.

Adding to a number of ad-hoc, proto-podcasting techniques for automatically downloading audio files, podcasting proper became popular through association with blogs (in particular MP3 blogs), the XML-based file format called RSS (Really Simple Syndication), and the polling applications called feed readers or news readers that poll and download RSS files.

Blogs, often being self-published websites, provided a convenient means for individuals to self-publish audio files online. RSS already gave websites and blogs a means to summarize or list new content added to the site. Individuals already used RSS to poll websites for new content. Thus, the addition of audio file listings to RSS, and the addition of audio file downloading to RSS feed readers built upon the feed reader's existing methods for polling and downloading files, and upon the existing "reader driven" interaction with content publishers.

Comparison to broadcasting and webcasting
Podcasting is different from broadcasting and webcasting in that it "casts" audio not by a mechanism of centrally pushing audio out to listeners, but by the mechanism of the (distributed) listeners pulling (downloading) the audio files automatically. Podcasters publish (or "podcast") audio files, even in the likeness of radio shows, but it is the individual listener who initiates the "cast" through their subscription and automatic download of the audio program.

Podcasting also utilizes the combination of audio files and RSS to publish descriptive data and metadata associated with the audio. RSS files used in podcasting include dates, titles, descriptions, and links to audio files. These links to audio files within RSS, which are used by podcasting applications, are defined by the enclosure elements in RSS 2.0 and RSS 1.0 (RDF), and all of the original podcasting proper applications were built to work with RSS 2.0.

*This information was obtained from Wikipedia, a free online encyclopedia.