Modem is short for Modulator/Demodulator.
Technically, a modem converts an analog signal to a digital one, and vice-versa. Originally modems were the devices that connected a computer to a telephone line and converted signals between audible tones that could be transmitted on a normal telephone equipment (POTS), and the digital signals required by computers. The act of converting a digital signal to audio is “modulation”, and the reverse is “demodulation” – hence the term.
The term is being commonly misused to refer to almost any device that converts between ethernet (the digital signal) and the various ways that connectivity is delivered by ISPs. DSL, cable and cellular modems may not actually convert to and from analog/audio tones, but between differing types of digital signals – a process where modulation and demodulation is not actually required.« Back to Glossary Index