Which term describes the practice of unsolicited advertisement via facsimile machines?

The term that describes the practice of unsolicited advertisement via facsimile machines is "Spam." In the context of fax communications, spam refers to bulk unsolicited faxes sent to multiple recipients who have not opted in to receive such communications. This practice is often viewed negatively because it clutters recipients' fax machines and wastes resources.

While "Commercial Messaging" and "Illegal Solicitation" might seem relevant, they are broader terms that do not specifically pinpoint the nature of unsolicited faxes. "TCPA Violation" relates to the Telephone Consumer Protection Act, which regulates certain types of telemarketing and fax communications, but it is a legal context rather than a term describing the act itself. Hence, "Spam" is the most accurate term used for unsolicited advertisements sent via fax, as it encompasses the idea of unwanted and often irritating bulk communications.