Fax (an abbreviation from facsimile) represents a document sent or received over a telephone line.
Nonetheless, nowadays fax files can also be sent using the Internet (called Internet faxing).
Internet fax has become very popular compared to the traditional fax due to the reduction of communication costs since the telephone connection charge no longer exists (only the Internet connection needs to be paid for).
The only pre-requisite for Internet fax to be efficient is for both the sender and the receiver computers to have dedicated fax software installed.