Channel 5, known as Five from 2002 until 2010 before reverting to its old name, was the last terrestrial television broadcaster to be launched in the United Kingdom. It went on air in late March 1997, starting with an exclusive Spice Girls video.
Britain's UHF transmitter network was originally designed to transmit four networks over most of the country. 5's frequencies had to be squeezed between the existing frequencies, often at lower power to avoid interference, and in some parts of the country its signal was weak or nonexistent. In addition, the frequency at which it was broadcast could cause interference with VCRs, leading to people around the country having to retune their VCRs. In order to increase its availability in these areas, it became the first terrestrial network to duplicate its programming on satellite. Today it is available on all digital platforms and analogue in some areas.
Unlike The BBC, ITV and Channel 4, Channel 5 was not organized by the British government. Although it uses public airwaves, and is therefore subject to public service broadcasting restrictions, Channel 5 has not had so many restrictions placed on its output as the other terrestrial channels.
The channel used to be notorious for its pornographic content after the Watershed, a reputation exacerbated by an exec who supposedly declared that the channel was about "the three F's -- films, football, and fornicating". She actually said that the channel was about "more than the three F's", but was misquoted. Whether the misquote was intentional, however...
Although some relics of this sordid past crop up every once in a while (the late night schedules are now mostly devoted to sport and Super Casino), Channel 5 is now best known as the British home of a number of U.S. crime dramas, including all three of the CSI Verse shows (with which it has a severe case of Adored by the Network). It's also shown FlashForward, The Mentalist, Grey's Anatomy, Thirty Rock, Law and Order, Charmed, NCIS, House, Californication, Xena: Warrior Princess, That '70s Show and others. (However, the channel has yet to demonstrate any real loyalty to any series which doesn't have "CSI" in the title -- 30 Rock, Charmed and House, among others, were all dropped; the channel also picked up Angel when Channel 4 let it go after its disastrous handling of the first season... and dropped it after the second.) Channel Five famously paid over the odds for Joey, a show which gave them one of their highest-ever audiences for the first episode...and then sank without trace.
It has two digital offshoot channels, "5USA" and "5*" (Five-star). The former shows a lot of U.S. imports, while the latter depends largely on Home and Away and Neighbours (although this also airs several American series, such as Archer and The Lying Game).
Channel 5 was formerly owned by the Radio Television Luxembourg RTL Group, who own a number of other European channels, but as of July 2010 is owned by British Newspapers baron Richard "Dirty" Desmond's Northern and Shell, owner of the Daily Express and Daily Star, plus a few more, shall we say, "adult" satellite channels.