Simply put, it's a means of using the Internet to reach a listening audience.

Net Radio is different things to different people - increasingly it offers previously impossible opportunities to individuals or small groups get heard, often broadcasting to more niche markets than ever before. Of course the big players are also involved, with many established terrestrial stations using the net to simulcast their exising output.

An excellent guide to some of the terminology used in this report is found here

In the UK 13% (6.5 million) of adults have used the Internet to listen to radio (RAJAR 2003) .

More than 100 million (20%) Amercians have tuned in online, 47 million (10%) doing so on a regular basis (Arbitron 2003), compared with 95% of US population who use conventional radio in a given week.

Live365 is the largest Internet radio hosting network, currently with over 30,000 stations, claiming an audience of more than 3 million listeners each month.

Most listening is done during office hours - one estimate is that 2% of America's midday broadcast radio audience is online (RAIN - 'Future of Internet Radio') .

"How do you define an Internet radio station.. is it four tracks on a loop, does it need a DJ, can you publish a playlist? These questions had never been asked before. Traditional radio and the licensing rules have grown up around the transmission radius of a transmitter, the difference once you move online is that it is global."

Gavin Starks, who helped found Virgin Radio's online presence, on some of the initial dilemma's surrounding net radio.

"A lot of people listen online because they cannot get it as a broadcast stream. Internet radio's there because you need to get that content but you cannot get it when you want to get it. The two biggest problems it faces are the rights to music royalties and the actual cost of delivering the streams."

Craig Moehl, Groovy Gecko Streaming Specialists.

"Monthly usage has really tripled in three years. Broadband is definitely a factor in it. It's also people being able to find content that they can't get elsewhere, and people are always looking for unique and interesting content."

Jodie Kahn, Arbitron - webcast ratings providers.