Perhaps the Internet's first four letter word...
According to spam.abuse.net, spam is defined as 'flooding the Internet with many copies of the same message,' hoping to force it on those who would otherwise choose not to read it. That's pretty much any message that can be mass-produced onto the Internet for public consumption, and in one way or another forced to the desktops and laptops of many unsuspecting victims.
It's become the virtual, cyber equivalent of junk mail and the term has in the past few years been used in more and more general ways. The definition has spread to encompass any unsolicited message, and now most commonly refers to automated, unwanted e-mail, typically advertisements and 'Make Money Fa$t!!!' scams.
'Spam' (as a net term) dates back to the very beginnings of the Internet, which also coincided, more or less, with the original broadcasting of England's comedy television programme Monty Python's Flying Circus. One of the show's most popular sketches featured a waitress in a diner, listing the day's specials for a customer. Most of the menu consisted of Spam® (the lunchmeat), and as the waitress repeated the word, the chant was taken up by a nearby group of Vikings, who lustily sang, 'Spam spam spam spam, spam spam spam spam, Lovely spam! Wonderful spam!' over and over until the waitress shouted at them to shut up.
As it happened, many computer programmers and hackers who were the first users of the Internet were also rabid Monty Python fans, and the worst trait of a rabid Python fan is the habit of constantly repeating favorite sketches, often in their entirety. Naturally, as soon as a newsgroup existed for the discussion of Monty Python, a message appeared that was nothing but 'spam spam spam spam spam spam spam spam' for pages and pages and pages. This message reappearred with some frequency, and eventually it started to be crossposted to other newsgroups that had nothing at all to do with Spam®, Python, or Vikings.
Thus, posting off-topic messages to newsgroups, particularly a large number at once, became known as 'spamming'. As technology continues to improve, finding new and better ways to get messages from one place to another rather quickly, spammers1 are simultaneously discovering new and better ways in which to spam.
The Costs of Spam
Vocal opponents of spam also point out that the price for sending this spam is inconsequential to the sender, but much of the cost inadvertently goes to the organisations that own and operate the hardware that gets the spam from point A to points B to Z. This cost is also inevitably trickled down to the consumer, ie, you and me.
The cost of all this talk about spam has perhaps been at the most expense to the corporate entity who owns the patent for Spam® and that cost is yet to be fully calculated. To their credit, Hormel Foods, has taken this in stride, and are probably aware of the old adage any free publicity is good publicity. Spam® was originally, and still is, a luncheon meat made by the Hormel Food Company. Consequently, Spam® is in itself probably the only foodstuff with a major international cult following.