Podcasting is a means of distributing audio and video programs via the Internet. It lets users subscribe to material that is output by individuals or organisations, have new material automatically downloaded to them, and then hear or view it at the time that they choose. Audio material is normally stored in a file format known as MP3 - the format used by Apple's iPod and other MP3 players.

Podcasting initially became popular in late 2004, largely due to software that enabled automatic downloading of audio both onto computers with suitable MP3 playback software and mobile devices that could play MP3 files.

Podcasting is distinct from other types of online media delivery because of its subscription model. The idea is to provide the material not as a one-time delivery, but rather to deliver files automatically over time as new material is added (known as a feed). Podcasting enables independent producers to create self-published, syndicated radio shows, and gives broadcast radio programs a new distribution method. Listeners may subscribe to feeds using "podcatching" software (such as Apple's iTunes software that is shipped with their iPod products), which periodically checks for and downloads new content automatically.

The word "Podcast" is often incorrectly used to describe the posting of any link to a media-player-compatible audio file (typically MP3) on a website. Some radio personalities post MP3 versions of their shows daily, and even though they are not part of any subscription model, they are often called podcasts.

Most podcatching software enables the user to copy podcasts to portable music players. Any digital audio player, MP3 player or computer with audio-playing software can play podcasts. Podcasting is a portmanteau that combines the words "broadcasting" and "iPod". The term can be misleading
since neither podcasting nor listening to podcasts requires an iPod or any portable player, and no broadcasting is involved.

Source: Wikipedia