jargon.artrocity.com
New Hacker's Dictionary the Jargon File v 4.4.6
A large, primitive, power-hungry active electrical device, similar in function to a FET but constructed out of glass, metal, and vacuum. Characterized by high cost, low density, low reliability, high-temperature operation, and high power dissipation. Sometimes mistakenly called a tube in the U.S. or a valve in England; another hackish term is glassfet.