An e-mail message sent to a large number of people without consent, also known as Unsolicited Commercial E-mail (UCE) or junk e-mail. Spam is usually sent to promote a product or service. It is also found in newsgroups, where people post identical and irrelevant messages to many different newsgroups that have nothing to do with the content of the posting. Some newsgroup users distinguish spam from velveeta (which is to cross-post to an excessive number of newsgroups), and consider spam to be worse because posting messages separately drains more disk space and network bandwidth.
As a broadcast, spam is characterized by its large volume. Spammers (people who spam) follow the traditional direct-marketing ploy of saturating the intended audience, hoping for a tiny return-from less than 1 percent up to 5 percent. Spammers don't care about the large number of people they irritate or offend, because there always seems to be those few people who visit their advertised Web site or order their product.
The term comes from "a Monty Python television show in which one particular episode made so many references to the canned meat product that the rest of the show was overshadowed by the spam motif." It is considered to be a serious violation of netiquette and many ISPs are utilizing anti-spam tools and methods fight and pursue spammers.
The most common forms of e-mail spam are:
Pyramid schemes (including Multilevel Marketing, or MLM);
Other "Get Rich Quick" or "Make Money Fast" (MMF) schemes;
Offers of phone sex lines and ads for pornographic Web sites;
Offers of software for collecting e-mail addresses and sending spam;
Offers of bulk e-mailing services for sending spam;
Stock offerings for unknown start-up corporations;
Contrary to popular belief, "spam is not protected by national Free Speech laws because free speech guarantees you the right to say what you want (within reason), it does not guarantee you a platform to make yourself heard in." For example, your "daily newspaper will take any commercial advertisement subject to two constraints: (a) it must fit within their advertising guidelines, and (b) the advertiser must pay for the costs of distribution. Spam fails on both of these counts." Also contrary to popular belief, "anti-spam is not censorship because censorship is blocking information based on its content whereas spam-blocking attempts to keep the content in its proper place." Another example, your "local public library has a bulletin board where people can post for-sale ads and business cards; they would be rightfully upset at someone who inserted an advertising flyer inside every book on the shelves, which is the equivalent of posting a notice to every Usenet group."
FYI: Canter and Siegel's seminal spam was propagated through Usenet and not email. The amount of spam that "spam king" Robert Alan Soloway, indicted under the CAN-SPAM Act, is accused of sending over a period of four years is now (in 2007) pumped out about every 30 seconds, around the clock, around the world. And, the U.S.'s first felony prosecution for sending spam involved Jeremy Jaynes, who received a 9 year prison sentence for sending junk e-mail. Jaynes was convicted of pumping out at least 10 million e-mails a day with the help of 16 high-speed lines.