A modem is a network device that converts digital data signals into analog signals that are transmitted over a telephone line or other analog communication channel. A modem allows a computer or other device connected to a network to transmit and receive data using analog communication lines.

Modems can have different data transmission speeds, typically measured in bits per second (bps). Previously, modems were commonly used to connect to the Internet via a telephone line, but with the advent of broadband Internet, modems are usually used to connect to other networks such as local area networks (LANs) and virtual private networks (VPNs).

Currently, modems can be embedded in other network devices such as routers or switches, which reduces the cost and number of necessary devices. Modems can also be connected to a computer using USB or Ethernet interfaces.

Modems are an important component of any network, especially for connecting to the Internet and other networks that use analog communication lines.