1. Acronym for MOulate DEModulate. Hardware that allows computers to interact with each other via telephone lines by converting digital signals to analog for transmission along analog lines. MOdulator/DEModulator, a gizmo which translates the digital information your computer produces into analogue signals that can be sent down the phone lines. From Glossary of Distance Education and Internet Terminology

2. Shorthand for MODulator/DEModulator, a modem allows the transmission of digital information over an analog phone line. A modem dictionary is available that defines all the basic terms. From KADOWKEV