Podcasting is emerging as a new killer application online, making its mark online.

The concept's hit a fast growing-curve. "Two weeks ago, the word 'podcasting' yielded 53,000 hits in the Google search engine. By Thursday, the number had nearly tripled", writes a US college newspaper. A search today shows 389,000 results - 389,001 now this report is up.

What is it? Podcasting harnesses the power of MP3 players, such as iPods, and lets users prerecord their own shows using a special RSS format that supports 'enclosures', such as audio. Influential blogger's site, Blogcritics considers the practice harnesses a similar creative need as iPod DJ clubs.

The technology has led to the online debut of an ever-growing number of special-interest 'virtual radio' shows, with a slight bias toward technology channels at present.

It's not all technology, one channel, Earnings Cast! downloads the audio of a corporate earnings phone call for later listening. Inside Mac Radio has also launched its own Podcast channel.

Former MTV host Adam Curry could be said to have got the ball rolling with his software application, iPodder. His daily Podcast, 'The Daily Source Code', now has 10,000 subscribers.

iPodder is like any other RSS newsreader, except it's capable of subscribing to and automatically downloading such presentations. Then, it automatically transfers these to iTunes, and these programmes are synched to a user's iPod for later listening.

Scripting News blog writer Dave Winer observed: "Blogging had to wait for press people to get it. This one doesn't have to wait".

"We now have a way of spreading something new very quickly," he said.