What are Podcasting and Internet Radio?

A friend emailed me this question. Here's my reply:

Podcasting and internet radio are both kind of vaguely defined terms right now - there can be more than one meaning.

Internet radio can mean continuously streaming audio either coming from a broadcast station onto the internet, or generated independently just for web streaming. But internet radio can also sometimes mean making pre-recorded audio files available for listening by streaming, and/or by downloading.

Podcasting generally refers to single items of audio - for example, a radio program. It can sometimes refer to streaming audio, sometimes to downloadable files that you access online, and sometimes also to a kind of automatic downloading system that delivers the audio directly to your computer or mobile device. The best known method for this automatic syndication is RSS - which supposedly stands for Really Simple Syndication. There are a few other computer applications now that do basically the same thing. The term Podcasting was created in conjunction with Apple's iTunes/iPod application, but it has been adopted to refer to pre-existing technology for audio file downloading and streaming, and also for newer technologies like RSS.

Someone needs to begin a good taxonomy of web applications, to help people figure out what they are describing and to aid in useful naming conventions. Perhaps such exists and I just haven't found it yet.