Spam - Unsolicited e-mail, often of a commercial nature, sent indiscriminately to multiple mailing lists, individuals, or newsgroups; junk e-mail
This one's origin had me in splits. Today's Yahoo news article on Spam being Hawaii's favorite food is what led me to it. Turns out Spam is the brand name of a canned seasoned pork product, created in the United States, which is really a portmanteau of "Spiced Ham". Because it wasn't rationed like beef, it was abundantly available and Spam became an all-American staple during World War II.
The term was supposedly coined from a Monty Python television skit in the early 1970s, in which every item on a restaurant menu contained SPAM, and there was nothing a customer could do to get a meal without it. A group of Vikings in the restaurant sing about the meat product, "Spam, spam, spam, spam, spam, spam, spam, spam, lovely spam! Wonderful spam!", to drown out all other conversation, until told to shut up. The word "Spam" is uttered at least 132 times. As a result, something that keeps being repeated to great annoyance was called spam, and computer programmers picked up on it.
Trivia: The Hormel company, the makers of the meat product Spam, while never quite happy with the use of the word spam for junk email, have always seemed supportive of Monty Python and their skit. The skit is part of the company's Spam museum in Austin, MN, United States and is performed every day by local actors.