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 card implements the electronic circuitry required to communicate using a specific physical layer and data link layer standard such as such as ethernet or token ring. This provides a base for a full network protocol stack, allowing communication among small groups of computers on the same LAN and large-scale network communications through routable protocols, such as IP.
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.