Spam: Spam is unsolicited messages, especially advertising, that are sent indiscriminately. It is economically viable for advertisers to send spam because there are no operating costs, beyond managing mailing lists. It is also very difficult to hold senders accountable for these mass mailings.
While email spamming is the most common form of spam, the term also applies to similar abuses in other media: instant messaging spam, search engine spam, spam in blogs, wiki spam, online classified ads spam, mobile phone messaging spam, Internet forum spam, junk fax transmissions, social spam, television advertising, and file sharing spam.
The costs of this spamming, such as lost productivity and fraud, are borne by the public and by Internet service providers, which have been forced to add extra capacity to cope with the deluge.
Spam can be used to spread computer viruses, trojan horses, or other malicious software. The objective may be identity theft, or worse.
In 2004, the United States passed the CAN-SPAM Act of 2003, which provided ISPs with tools to combat spam. This law has been criticized by many for not being effective enough, and is indeed supported by some spammers and organizations who support spamming.
Spam is named after the lunch meat, by way of a Monty Python sketch in which Spam is included in every dish.