Spam is not, as some people believe, an acronym for Short, Pointless, and Annoying Messages. The word is related to the name of the luncheon meat sold by Hormel since 1937, a portmanteau from SPiced hAM. But how did it come to refer to e-mailed invitations to enlarge the male member and share the ill-gotten gains of deposed African despots? Many people assume that the route was metaphor. Like the luncheon meat, the e-mail is cheap, plentiful, and unwanted, and in one variant of this folk etymology, spamming is what happens when you dump Spam in a fan. Through these intuitions may have helped make the word contagious, its origin is very different. It was inspired by a sketch from Monty Python's Flying Circus in which a couple enter a café and ask the waitress (a Python in drag) what's available. She answers:

Well, there's egg and bacon; egg sausage and bacon; egg and spam; egg bacon and spam; egg bacon sausage and spam; spam bacon sausage and spam; spam egg spam bacon and spam; spam sausage spam spam bacon spam tomato and spam; spam spam spam egg and spam; spam spam spam spam spam spam baked beans spam spam spam, or Lobster Thermidor: a Crevette with mornay sause served in a Provençale manner with shallots and aubergines garnished with truffle pâté, brandy and with fried egg on top and spam.

You are probably thinking, "This sketch must be stopped - it's too silly". But it did change the English language. The mindless repetition of the word spam inspired late-1980's hackers to use it as a verb for flooding newsgroups with identical messages, and a decade later it spread from their subculture to the populace at large.

Steven Pinker: The stuff of thought, Language as a window into human nature, Viking, New York, 2007.