What's a Modem ? (this is really fun)

If you are subscribed to the internet, there is a modem in your house. This is a black box (with blinking lights) which converts the signal coming into the house, to a usable signal for your computer.

It is probably also transmitting that signal via wifi, to your computer

Here is Wikipedia's quick explanation

A modem (modulator-demodulator) is a network hardware that modulates one or more carrier wave signals to encode digital information for transmission and demodulates signals to decode the transmitted information. The goal is attempting to produce a signal that can be transmitted easily and decoded to reproduce the original digital data.