Definition: A podcast is a pre-recorded audio program that's posted to a website and is made available for download so people can listen to them on personal computers or mobile devices.
Podcasting takes its name from Apple's popular iPod line of products, but it isn't limited only to iPod owners and listeners. What distinguishes a podcast from other types of audio products on the internet is that a podcaster can solicit (=ask for, request) subscriptions from listeners, so that when new podcasts are released, they can automatically be delivered, or fed, to a subscriber's computer or mobile device. Usually, the podcast features an audio show with new episodes that are fed to your computer either sporadically (sometimes, at irregular intervals) or at planned intervals, such as daily or weekly. Just like the old radio serials of the 1930s and 40s, this format encourages listeners to subscribe (=sign up so you can get every show) so they can find out "what happens next."
As long as you listen to podcasts only on your computer (the vast majority of podcast subscribers do), you don't need any special software other than the audio player, such as a Windows Media Player or RealPlayer, you already have on your computer. But if you want to subscribe to a podcast feed, you'll need to install "podcatcher" software on your computer. The most popular podcatcher software is iTunes.
Do you ever listen to podcasts? For what purpose?