The term podcasting comes from combining the words iPod and broadcasting. Podcasts are largely MP3 files like the ones played on the Apple iPod, and they're available for free or broadcast over the Web.
In fact, you don't need an iPod to listen to podcasts (the term podcast is misleading because it suggests that you do). You don't even need a portable player if you have a computer that plays audio. The truth is that experiments with video enclosures in RSS date back to 2000. Some people, who don't like the name podcasting because it suggests a connection to Apple, call it blogcasting, audioblogging, RSScasting, or Webcasting.
A podcast is simply an RSS feed on the Internet that includes audio and/or video files and that can be publicly subscribed to. It's different from the other type of online audio or video distributionstreaming audio or videobecause when you stream audio or video, you download the data and there's no file involved; if you want to save the data, you have to capture it and store it in a file. With podcasting, your computer downloads the entire file first, then plays it (unlike with streaming, where the playback can begin as soon as you start downloading data). Podcasts can't be used to broadcast live events, as streaming can. Instead, podcasts are meant to distribute subscribed content.
The popularity of podcasting is enormous. According to online encyclopedia Wikipedia, blogger Doc Searls has been keeping track of the number of podcast entries in Google since September 28, 2004. At that point, he found 24. On September 30, there were 526. Three days later, there were 2,750. By October 18, there were over 100,000. A year later, Google listed more than 100,000,000 entries for podcast.
It's also worth noting that although podcasts are usually MP3 sound files or MPG or MP4 video files, they can be any file type, such as PDF. XML files, such as RSS files, can't contain binary data such as the data stored in audio or video filesthey can contain only text. However, they can point to binary files (such as MP3 files) with the URL of those files, and that's exactly what happens with podcasting.
This example includes an enclosure named snow.mp3:
<item> <title>Steve shovels the snow</title> <author>email@example.com</author> <description><![CDATA[It snowed once again. Time to shovel!]]></description> <pubDate>Thu, 08 Dec 2005 08:39:51 -0500</pubDate> <link>http://www.rssmaniac.com/steve</link> <enclosure url="http://www.rssmaniac.com/steve/snow.mp3" length="4823902" type="audio/mpeg" /> </item>