proprietary name registered by Geo. A. Hormel & Co. in U.S., 1937; probably a conflation of spiced ham. Soon extended to other kinds of canned meat.
In the sense of "internet junk mail" it was coined by Usenet users after March 31, 1993, when Usenet administrator Richard Depew inadvertently posted the same message 200 times to a discussion group. The term had been used in online text games, and ultimately it is from a 1970 sketch on the British TV show "Monty Python's Flying Circus" wherein a reading of a restaurant's menu devolves into endless repetitions of "spam."