The sale of wireless spectrum has been very much in the news lately. Interesting phrases such as 'red underpants' and 'waterfront property' have been thrown around as government, businesses and the media prepare for the multi-billion-dollar spectrum auctions on April 16. Telstra, Optus and Vodafone have all confirmed they'll take part in the auctions, despite being annoyed at prices that are reportedly 3.5-times greater than those in comparable countries. So with this in mind, it might be useful to explain just what 'spectrum' is and how it relates to mobile communications.