In telecommunication, a hotline (also called an automatic signaling service or off-hook service) is a point-to-point communications link in which a call is automatically originated to the preselected destination without any additional action by the user when the end instrument goes off-hook.
Hotlines cannot be used to originate calls other than to preselected destinations. Various priority services that require dialing are not properly termed "hotlines."
Perhaps the most famous hotline linked the White House with the Kremlin during the Cold War. It was established in 1963 after the Cuban missile crisis made it clear that reliable, direct communications between the two great powers was a vital necessity.
Source: from Federal Standard 1037C
Hotline is also a pioneering file sharing and peer-to-peer tool which offers central servers over the Hotline protocol, and several clients.
wikipedia.org dumped 2003-03-17 with terodump