A modem is a device that connects your computer or network to the internet. It converts digital data from your device into analog signals that can travel over telephone lines or cable systems. This process allows you to send and receive information online, enabling activities like browsing the web, streaming videos, and sending emails. There are different types of modems, including DSL modems, which use telephone lines, and cable modems, which connect through cable television lines. Some modems also include built-in routers, allowing multiple devices to connect to the internet wirelessly.