A podcast is a collection of media files served over the world wide web using an XML-based syndication format such as RSS or Atom. The content provider makes available an RSS feed listing - usually in reverse chronological order - the most recent audio or video releases. Having subscribed to this feed, a podcatcher such as iTunes, Miro or iPodderX checks the feed periodically and downloads any new content it finds, and optionally syncs this with a portable digital audio device like the iPod. The invention of podcasting has been disputed, but Dave Winer seems to have pioneered the concept in 2004, working alongside Adam Curry.
A large number of podcasts have been created - a mixture of professional, mainstream media podcasts from organisations like the BBC, PBS and commercial broadcasters, and amateur creations by hobbyists and bloggers. Unlike radio, they are not tied to any specific requirement in terms of frequency of updates or length of shows - thus allowing people to have more sporadic and informal diary shows. A vibrant podcaster community has grown up with the medium, which includes conferences like PodCamp, podcast networks for niche interests (QPodder, the StarQuest Podcast Network and the Tripod Network are examples, covering the GLBT community, Roman Catholicism and science/technology respectively). The low entry cost and global reach has allowed niche interest podcasts to flourish.