A modem, short for MOdulator/DEModulator, is a device that connects a computer to a telephone line, enabling access to the Internet or the sending and receiving of faxes. It works by converting digital data from the computer into analogue signals suitable for transmission over phone lines, and then reconverting incoming analogue signals back into digital form.
Modems are available in both internal and external versions, with external units typically housed in small boxes connected via cables. While modern broadband and mobile connections have largely replaced traditional dial-up modems, understanding this technology is still useful for historical context and certain niche applications.