Without context, the question is a bit vague and I may not give the best answer, but in general terms, I would say the answer is a Network Interface Card (NIC) or an Ethernet card.
An Ethernet card is one of a network adapter. It is a physical expansion card that inserts into the PCI expansion slot on a PC and is used to transmit data from the network into the computer. It is connected to the computer using an Ethernet cable.