transceiver

Device used in networking that does the actual signalling over the media. In Ethernet, it plugs into an AUI port. This can also refer to a radio which can both transmit and receive, like a CB Radio.

An Ethernet Network Interface Card, or NIC, can have an external AUI transceiver plugged into an Ethernet card (assuming it is an older 10base5 or combo 10base5 + 10baseT card), but most common NICs have them built into the card.

10baseT, which uses twisted-pair wiring, and 10base2, which uses thin coaxial cable attached to a Tee connector, have their transceivers built into their NIC. Some NICs have connections for both, and are called combo NICs

Transceiver is a combined word, taken from Transmitter and receiver. To save on manufacturing costs, a separate transmitter and receiver is combined into one package. This allows common modules to be shared between the transmitting portion and the receiving portion.

Refer to How Network Adapters Work and network topologies for additional information.

Just to add a bit, the original use of the term transceiver was to describe analog voice radios. Early radio sets were extremely bulky due to the use of vacuum tube components. Sets that could both receive and transmit were specified as 'different' since usually only one or the other was possible.