What is a modem?

modem n. a communications device used to connect computers via telephone lines.

"Modem" is an acronym for MOdulate-DEModulate. A modem is a device or program that enables a computer to transmit data over telephone lines.

Computer information is stored digitally, whereas information transmitted over telephone lines is transmitted in the form of analog waves. A modem converts data from analog to digital and vice versa (modulating and demodulating), thus enabling two computers to communicate with each other over a phone line.