A modem (modulator-demodulator) is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information.
The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data.
Modems can be used over any means of transmitting analog signals, from light emitting diodes to radio.
Fix Modem issues on Windows 10
Here are some useful guides to help you fix common modem issues on Windows PC.