Modem

A modem ("modulator-demodulator") is a device that converts digital information to analog signals and vice versa, for sending data through networks.

Different kinds are used for different networks: DSL modems for telephone wires, Wi-Fi modems for short-range wireless radio signals, 3G modems for cellular data towers, and so on.

Modems are different from routers, but many companies sell modems combined with routers.