Podcasting, according to Wikipedia, is "the practice of making audio files available online in a way that allows software to automatically detect new files and download them." Technically this is accomplished using RSS feeds to provide information about a collection of audio files in MP3 format. The term podcasting is often used to refer to one off audio broadcasts that can be downloaded from the Internet although this is not, strictly speaking, a true podcast which should be a ‘series’ of broadcasts.
Podcasting lets anybody with a microphone; a computer and an Internet connection publish audio broadcasts that can be listened to by people anywhere in the world. Because the barriers to entry are very low, podcasting is rapidly becoming a popular way for people to share audio broadcasts. Podcasts are free and can be automatically downloaded to portable media players, so they can be listened to whenever it’s convenient.