Generally a podcast refers to an episode or a series of audio files delivered over the internet. These audio files may also be listened to in a browser or with a podcatcher such as iTunes on a computer or mobile device.
According to Google:
a digital audio file made available on the Internet for downloading to a computer or portable media player, typically available as a series, new installments of which can be received by subscribers automatically.
and:
A podcast is a digital medium that consists of an episodic series of audio, video, digital radio, PDF, or ePub files subscribed to and downloaded through web syndication or streamed on-line to a computer or mobile device. The word is a neologism and portmanteau derived from “broadcast” and “pod” from the success of the iPod, as audio podcasts are often listened to on portable media players.mp3
