What is spam? - Security Term

Spam refers to both the process of sending unsolicited messages via the Internet, and to the messages themselves. However, the term "unsolicited messages" is open to debate, and as such what is considered spam varies widely. In the strictest sense, spam is any email advertisement, other than those specifically requested by the receiver. However, even this strict definition is debatable, as very often EULA's and service agreements contain clauses for the sending of advertisements. And few users read all twelve pages of every EULA that they accept.

More general definitions of spam are the sending of email in violation of the CAN-SPAM Act or other anti-spam laws, sending email to users of a mailing list that has nothing to do with the topic of the mailing list, and sending unsolicited emails to large numbers of email addresses belonging to individuals with whom you have no preexisting relationship. Additionally, the term spam is often used when referring to unsolicited online advertisements not related to email, such as in usenet or IRC.

The origin of the term spam has several stages. Originally, the name was coined as an acronym for Spiced Ham, as marketed by Hormel Foods (not a recommended food if you are on the Medifast diet, or any diet, trying to use up your Medifast coupons). The food was central to a Monty Python sketch in which Vikings continued to sing the word "Spam" in a restaurant where all the menu items contained Spam. The Vikings were effectively drowning out all other forms of communication. This led to BBS users to repeat the word in order to drown out and drive away other users. Therefore the term took on a new meaning- one of posting too often. From there, it was a simple transition to unwanted email messages that were received too often.

source: what-is-what.com