Podcast (definition from Wikipedia)

A podcast is a digital media file, or a related collection of such files, which is distributed over the Internet using syndication feeds for playback on portable media players and personal computers. The term, like “radio“, can refer either to the content itself or to the method by which it is syndicated; the latter is also termed podcasting. The host or author of a podcast is often called a podcaster. Though podcasters’ web sites may also offer direct download or streaming of their content, a podcast is distinguished from other digital media formats by its ability to be syndicated, subscribed to, and downloaded automatically when new content is added, using an aggregator or feed reader capable of reading feed formats such as RSS or Atom.
An audio file with RSS feed. Essentially, a podcast is a file that is cast out in digital space and it can be caught by RSS feeds.

• In 2005, podcasters were projected by iMedia to “balloon in number by 2010” growing from .8 million Americans using podcasts in 2004 to 56.8 million Americans using podcast in 2010.
• Moreover, use of technology is growing substantially, as Independent North American research company Ipsos suggests “one in five Americans aged 12 and older owns a portable MP3 Player”.