A network card, network adaptor or NIC (network interface card) is a piece of computer hardware designed to allow computers to communicate over a computer network or connect. Access to the internet is possible when the network is connected to a cable or DSL modem.

http://en.wikipedia.org/wiki/Network_card

Wireless:
Typically networks use special cables to connect each computer to one another or to devices such as hubs, switches and routers. But with a wireless network adaptor or wireless network interface controller (WNIC) uses a radio-based computer network. Wireless networks require a wireless hub, wireless router or wireless modem for them to connect to the Internet or other computers on the network.

http://en.wikipedia.org/wiki/Wireless_network_interface_card

Also see:

http://en.wikipedia.org/wiki/LAN