A network card (also called network adapter, network interface [card], etc.) is a piece of computer hardware designed to provide for computer communication over a computer network.
The communication is usually carried out in accordance with a certain protocol such as ethernet or token ring among small groups of computers on the same LAN, and through a routable protocol, such as IP, for large-scale network communications.
A network card typically has a twisted pair or BNC connector socket where the network cable is connected, and a few LEDs to inform the user of whether the network is active, and whether or not there is data being transmitted on it.