A network card (also called network adapter, network interface [card], etc.) is a piece of computer hardware designed to utilize the machine with means 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.
A network card typically have a twisted pair or BNC connector socket where the network is connected, and a few LEDs to inform the user of whether the network is alive, and whether or not there is data being transmitted on it.