Podcasting is the method of distributing multimedia files, such as audio programs or music videos, over the Internet using either the RSS or Atom syndication formats, for playback on mobile devices and personal computers. The term podcast, like 'radio', can mean both the content and the method of delivery. The host or author of a podcast is often called a podcaster. Podcasters' web sites may also offer direct download or streaming of their files; a podcast however is distinguished by its ability to be downloaded automatically using software capable of reading RSS or Atom feeds.
Usually a podcast features one type of 'show', with new episodes released either sporadically or at planned intervals such as daily or weekly. In addition, 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 or watch when they want, where they want, and how they want.

"Podcasting" is a compound word coined in 2004 (see "History" below), that combined two words: "iPod" and "broadcasting."

While the name was primarily associated with audio subscriptions in 2004, the RSS enclosure syndication technique had been used with video files since 2001, before portable video players were widely available. Atom, a recently developed web syndication format, supports rich media content by design, as does standard RSS 2.0 based upon XML 1.0 standards. In fact, any file with a URL, including still images and text, can be delivered via a web feed.

The use of "podcast" to describe both audio and video feeds seemed natural to some users, while others preferred to reserve the word for audio and coin new terms for video subscriptions. Other "pod-" derived neologisms include "podcasters" for individuals or organizations offering feeds and "podcatchers" for special RSS aggregators with the ability to transfer the files to media player software or hardware.

Neither podcasting nor listening to podcasts requires an iPod or other portable player, and no over-the-air broadcasting is required. In fact, some believe that more people listen to podcasts on personal computers more often than on portable devices [citation needed]. The name association came about simply because Apple Computer's iPod was the most marketed and the best-selling portable digital audio player when podcasting began, and was used by early practitioners.

However, the use of the "pod" name in 2004 probably played a part [1] in Apple's development of podcasting products and services in 2005, further linking the device and the activity in the news media. The editors of the New Oxford American Dictionary declared "podcasting" the 2005 word of the year, defining the term as "a digital recording of a radio broadcast or similar program, made available on the Internet for downloading to a personal audio player".[2] From the beginning various writers suggested other names or alternative interpretations of the letters "P-O-D." Technology writer Doc Searls had proposed "Personal Option Digital" in September, 2004. [3] The "Personal on Demand" interpretation was in international circulation as early as October 2004.[4] In July 2005, Microsoft blogger Robert Scoble mentioned that interpretation while countering reports that his company was pushing the word "blogcasting" to avoid mentioning an Apple product.[5] "Blogcasting" also implied content based on, or similar in format to, blogs, which was not always the case.

Other terms have been suggested, but had shortcomings -- "audioblogging", "audio magazines" and "webcasting" could describe other forms of media distribution, and "rsscasting" would be difficult to pronounce.

Podcasting as a medium was first associated with, but never limited to, audio data. As use of RSS enclosures for video spread in 2005, podcasting of video data was called, among other things, "video blogging", "video podcasting", "vidcasting", "vlogging", "vodcasting", "vicasting", or "videocasting".

The publish/subscribe model of podcasting is a version of push technology, in that the information provider chooses which files to offer in a feed and the subscriber chooses among available feed channels. While the user is not "pulling" individual files from the Web, there is a strong "pull" aspect in that the receiver is free to subscribe to (or unsubscribe from) a vast array of channels. Earlier Internet"push" services (e.g., PointCast) allowed a much more limited selection of content.

Podcasting is an automatic mechanism by which multimedia computer files are transferred from a server to a client, which pulls down XML files containing the Internet addresses of the media files. In general, these files contain audio or video, but also could be images, text, PDF, or any file type.

A podcast is generally analogous to a recorded television or radio series.

The content provider begins by making a file (for example, an MP3 audio file) available on the Internet. This is usually done by posting the file on a publicly-available webserver; however, BitTorrent trackers also have been used, and it is not technically necessary that the file be publicly accessible. The only requirement is that the file be accessible through some known URI (a general-purpose Internet address). This file is often referred to as one episode of a podcast.

The content provider then acknowledges the existence of that file by referencing it in another file known as the feed. The feed is a machine-readable list of the URIs by which episodes of the show may be accessed. This list is usually published in RSS format (although Atom can also be used), which provides other information, such as publish dates, titles, and accompanying text descriptions of the series and each of its episodes. The feed may contain entries for all episodes in the series, but is typically limited to a short list of the most recent episodes, as is the case with many news feeds. Standard podcasts consist of a feed from one author. More recently multiple authors have been able to contribute episodes to a single podcast feed using concepts such as public podcasting and social podcasting.

The content provider posts the feed to a known location on a webserver. (Unlike the episode file itself, the feed is published to a webserver, usually not by other means.) The location at which the feed is posted is expected to be permanent. This location is known as the feed URI (or, perhaps more often, feed URL). The content provider makes this feed URI known to the intended audience.

A consumer enters this feed URI into a software program called a podcatcher or aggregator (the former term is specific to podcasting while the latter is general to all programs which collect news from feeds). This program retrieves and processes data from the feed URI.

A podcatcher is usually an always-on program which starts when the computer is started and runs in the background. It manages a set of feed URIs added by the user and downloads each at a specified interval, such as every two hours. If the feed data has substantively changed from when it was previously checked (or if the feed was just added to the podcatcher's list), the program determines the location of the most recent item and automatically downloads it to the user's computer. Some podcatchers, such as iTunes, also automatically make the newly downloaded episodes available to a user's portable media player. (This is only the typical behavior of a podcatcher; some podcatchers behave—or can be set to behave—differently.)

The downloaded episodes can then be played, replayed, or archived as with any other computer file.

Variants of the podcast include the marcast or Podcast Marketing. Podcast Marketing is the method of creating and publishing audio and video programs via the Internet. It allows a company's or marketer's users, clients, and customers to subscribe to a feed of new information about products and services.

To conserve bandwidth, users may opt to search for content using an online podcast directory. Some directories allow people to listen online and initially become familiar with the content provided from an RSS Feed before deciding to subscribe and then downloading a huge amount of content, only to find out later that they didn't have any interest. For most broadband users, bandwidth is generally not a major consideration; however, there are still a number of computers that are connected to the Internet using a dial-up connection.

Podcasting's initial appeal was to allow individuals to distribute their own "radio shows," but the system is increasingly used for other reasons, including:

A way for people and organizations to avoid regulatory bodies, such as the British Ofcom, that would not allow a program to be broadcast in traditional media.

A way for news organizations to distribute audio or video as an addition to their existing text (or mostly text) news products. For example, Wikinews began to podcast its News Briefs in 2005. Companies are also using podcasts as a way to distribute their multimedia news to journalists and consumers through companies like MultiVu.

Education. In 2004 Musselburgh Grammar School pioneered podcast lessons with foreign language audio revision and homework [6], other pioneers include The Room 208 Podcast, Radio WillowWeb, and Room 613 Talk. In the second half of 2005, a Communication Studies course at the University of Western Australia (iGeneration: Digital Communication and Participatory Culture) used student-created podcasts as the main assessment item. On the 21st February 2006 Lance Anderson, Dr. Chris Smith, Nigel Paice and Debbie McGowan took part in the first podcast forum at Cambridge University. The event was hosted by the Centre for Applied Research in Educational Technologies.

Politics. In the U.S., both major political parties have various podcasts, as do numerous politicians.

Religion. Godcasting has been used by many religious groups [7]. Many churches produce podcasts of talks and sermons. Disciples with Microphones provides podcasts relating to the Catholic Church.

Pornography. Porncasting and podnography are sometimes used to refer to pornography in podcasts.

Unofficial audio tours of museums.

Official cultural or historic audio tours of cities.

Communication from space. On 7 August 2005. American astronaut Steve Robinson claimed the first podcast from space during the Space Shuttle Discovery mission STS-114 - although there was no subscription feed, merely an audio file that required manual downloading. (transcript & audio).

Television commentary. Battlestar Galactica writer and executive producer Ronald D. Moore creates commentary podcasts for each new episode of Battlestar Galactica (download audio commentary). Other television shows have since followed suit.

Sports. In 2005, unofficial podcasts for major sports teams launched, providing fans both in and outside of the teams' direct broadcast areas with on-demand commentary. Pioneers include Cubscast. The Cubscast founders also formed the first city-specific sports podcast network, hosting one podcast for each major Chicago team at Chicagosportscasts.com.

Conference and meeting alerts. Podcasts can be packaged to alert attendees to agendas, hosted roundtables and daily feedback.

Advocacy. The 5,500 locked out staff (editors, journalists, technicians, hosts, etc.) of the Canadian Broadcasting Corporation were podcasting news and other programming during August and September of 2005.

Youth media. Podcasting has become a way for youth media organizations, such as Youth Radio (Youth Radio site), to bring youth perspectives to a wider audience.

Newspapers. Newspapers use podcasts to broadcast audio content from print interviews and drive traffic to their websites. The San Francisco Chronicle is believed to be the first major daily newspaper to start podcasting using an external website[10], in Feb 2005. Hong Kong's South China Morning Post was the first to use its own website and the first in Asia, having launched on April 19, 2005[.

Academic journal digests: The Society of Critical Care Medicine has a podcast used to update clinicians with summaries of important articles, as well as interviews.

Public libraries can podcast local publications free of Copyright, offering spoken word alternatives to the visually impaired. Non-profit organizations like Assistive Media podcast readings of short-format magazine articles for visually impaired readers.

Law enforcement. The Chicago Police Department has a free video podcast of its half-hour weekly news magazine called "CrimeWatch," which airs on local TV. It documents community policing (CAPS) success stories.

Replacement for live music audio streams. Whereas streaming a performance live over the Internet requires careful coordination of man and machine, podcasting offers the ability to do slight time-shifting of performances and greatly reduces the complexity of the effort. The quality of the program is often higher as post-production adjustments can be made prior to release. For example, programs such as the Woodsongs Old Time Radio Hour provide a live stream of their program, but most listeners don't hear it until weeks later on NPR. Podcasted versions of the programs split the difference, usually coming out a few days after the live program, but well before the traditional broadcast.

As a platform for alternate DVD commentary tracks (Audio commentary). Enables fans to add their own comments and thoughts to any of their favourite films.

As a way to teach how to use a computer. Through screencasting, many video podcasts, such as ScreenCastsOnline, demonstrate how to use software and operating systems.