Relating to email and the Internet, how did the terms "spam" and "spamming" come to be used?

Answer 1

Spam is a junk food, made out of who-knows what. In the world of cybergeeks it's common to use slang terms for just about everything. So applying the term 'spam' to junk messages made out of who-knows-what was just natural.

And of course there is the Monty Python SPAM sketch. Many believe that's the ultimate source of the term. The following is from Wikipedia:
Main article: History of spamming

The term spam is derived from the Monty Python SPAM sketch, set in a cafe where nearly every item on the menu includes SPAM luncheon meat. As the server recites the SPAM-filled menu, a chorus of Viking patrons drowns out all conversations with a song repeating "SPAM, SPAM, SPAM, SPAM... lovely SPAM, wonderful SPAM," hence "SPAMming" the dialogue. The excessive amount of SPAM mentioned in the sketch is a reference to British rationing during World War II. SPAM was one of the few foods that was not restricted and was therefore widely available.

Although the first known instance of unsolicited commercial e-mail occurred in 1978 (unsolicited electronic messaging had already taken place over other media, with the first recorded instance being via telegram on September 13, 1904), the term "spam" for this practice had not yet been applied. In the 1980s the term was adopted to describe certain abusive users who frequented BBSs and MUDs, who would repeat "SPAM" a huge number of times to scroll other users' text off the screen.