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 it was from the comedy routine in British TV show "Monty Python's Flying Circus" (beloved by many intellectual geeks) where a restaurant's menu items all devolve into spam.
To send a computer message out to myriad people: the cost to spam an advertisement in thousands of news groups is typically less than $50/ Spamming. Sending out on the Internet the cyberspace equivalent of junk mail
[1990s+ Computer; fr Spam, trademark for a brand of canned meat, which acquired a probably undeserved unsavory reputation among WWII troops]