n. The Tech Model Railroad Club at MIT, one of the wellsprings of hacker culture. The 1959 'Dictionary of the TMRC Language' compiled by Peter Samson included several terms which became basics of the hackish vocabulary (see esp. foo and frob).
By 1962, TMRC's legendary layout was already a marvel of complexity. The control system alone featured about 1200 relays. There were scram switches located at numerous places around the room that could be pressed if something undesirable was about to occur, such as a train going full-bore at an obstruction. Another feature of the system was a digital clock on the dispatch board. Normally it ran at some multiple of real time, but if someone hit a scram switch the clock stopped and the display was replaced with the word 'FOO'.
Steven Levy, in his book 'Hackers' (see the Bibliography), gives a stimulating account of those early years. TMRC's Power and Signals group included most of the early PDP-1 hackers and the people who later bacame the core of the MIT AI Lab staff. Thirty years later that connection is still very much alive, and this lexicon accordingly includes a number of entries from a recent revision of the TMRC Dictionary.