A modem, short for modulator-demodulator, is a device that converts data from a digital format into a format suitable for an analog transmission medium such as telephone or radio. It is a device that connects your home to your internet service provider (ISP) through a physical connection. The modem translates the data from your ISP into a format that your home network devices can use. There are three common types of modem connections: dial-up, DSL, and cable. Most ISPs will either rent you a modem or sell you one outright. Many modems nowadays are "all-in-one" devices that also include a router, although you can still purchase a modem and router separately.
In summary, a modem is a device that connects your home to your ISP and translates the data from your ISP into a format that your home network devices can use.
