Podcasting is defined as distributing audio or video files, such as radio programs or music videos over the Internet using either RSS or Atom syndication for listening on mobile devices and personal computers. The term podcast, like "radio", can mean both the content and the method of delivery. Podcasters' websites also may offer direct download of their files, but the subscription feed of automatically delivered new content is what distinguishes a podcast from a simple download or real-time streaming. Usually, the podcast features one type of "show" with new episodes either sporadically or at planned intervals such as daily, weekly, etc. In addition to this, there are podcast networks that feature multiple shows on the same feed.
Podcasting's essence is about creating content (audio or video) for an audience that wants to listen when they want, where they want, and how they want.
Apple, iTunes and Podcasting
With the introduction of podcasting in iTunes 4.9, Apple opened the floodgates to the world of podcasting. Literally overnight, more and more Mac users were subscribing to podcasts, and new podcasts were churned out at a notable rate. Apple further made podcasting easier accessible to the general public when it integrated podcast-recording features in GarageBand 3 in January 2006.
Large directories of podcasts can be found at podcast networks
Apple also offers podcasts, searchable via ITunes