any mail or letters that are not welcome or solicited and typically sent in bulk; especially mail of a commercial nature such as advertising circulars and form letters
An unsolicited and typically unwelcome message, often commercial or political in nature, transmitted via the Internet as a mass mailing (sometimes as if from a fictitious user or domain) to a large number of recipients.
In some countries so much advertising comes through the mail that many recipients proceed directly from the mailbox to the nearest wastebasket to toss out the junk mail.