Unwanted or unsolicited e-mail messages
Spam is unwanted or unsolicited e-mail messages from someone you do not know or with whom you do not have an established business or personal relationship. Spam is the electronic equivalent of junk mail. E-mail that is not requested. Spam is used to advertise products or to broadcast some political or social commentary.
The word Spam as applied to Email means Unsolicited Bulk Email ("UBE"). Also known as "unsolicited commercial e-mail" (UCE), "gray mail" and just plain "junk mail,". Unsolicited means that the Recipient has not granted verifiable permission for the message to be sent. Bulk means that the message is sent as part of a larger collection of messages, all having substantively identical content. A message is Spam only if it is both Unsolicited and Bulk.
Technical Definition of Spam
An electronic message is spam if:
(1) the recipient's personal identity and context are irrelevant because the message is equally applicable to many other potential recipients;
2) the recipient has not verified or granted deliberate, explicit, and still-revocable permission for it to be sent. Spam is an issue about consent, not content. If sent without consent of the recipient, it is spam. Whether the message is an advert, a scam, porn, a begging letter or an offer of a free lunch, the content is irrelevant - if the message was sent unsolicited and in bulk then the message is spam.
Spam is not a sub-set of UBE, it is not "UBE that is also a scam or that doesn't contain an unsubscribe link", all email sent unsolicited and in bulk is Spam.
This distinction is important because legislators spend inordinate amounts of time attempting to regulate the content of spam messages, and in doing so come up against free speech issues, without realizing that the spam issue is solely about the delivery method.
Other facts relating to spam: