A fax number is a phone number used by a facsimile, or fax, machine, sometimes also called a telefax or telecopy machine. A fax machine uses a series of signals to transmit a document from one location to another.
Fax machines, invented in the 1960s, were widespread at the end of the twentieth century, especially in business contexts. With the rise of ubiquitous broadband Internet service, they have largely been overtaken by other solutions. Some countries do not recognize the legality of signed documents sent over the Internet, while they do for faxed documents, so some businesses still use fax machines.