What is Modem?

The modem is the box that converts your ISP's line (cable, fibre, DSL) into a standard network connection. The router then shares that connection to all your devices. Many ISP boxes combine both jobs in one unit.

Why it matters: if Wi-Fi works but the internet is down, the fault is modem-side (or the ISP). Combined units can usually run in "bridge mode" so you can add your own better router.