A transceiver is a device that has both a transmitter and a receiver which are combined and share common circuitry or a single housing. If no circuitry is common between transmit and receive functions, the device is a transmitter-receiver. The term originated in the early 1920s. Technically, transceivers must combine a significant amount of the transmitter and receiver handling circuitry. Similar devices include transponders, transverters, and repeaters.
In radio terminology, a transceiver means a unit which contains both a receiver and a transmitter. It was quite common to have these units separated. Ham radio operators can build their own equipment and it is always easier to design and build a simple unit having one of the functions, transmitting or receiving. Almost every modern amateur radio equipment is now a transceiver but there is an active market for pure radio receivers, mainly for Shortwave listening operators. An example of a transceiver would be a walkie-talkie, or a CB radio.
On a wired telephone, the handset contains the transmitter and receiver for the audio and in the 20th century was usually wired to the base unit by Tinsel wire. The whole unit is colloquially referred to as a “receiver.” On a mobile telephone or other radiotelephone, the entire unit is a transceiver, for both audio and radio.
A cordless telephone uses an audio and radio transceiver for the handset, and a radio transceiver for the base station. If a speakerphone is included in a wired telephone base or in a cordless base station, the base also becomes an audio transceiver in addition to the handset.
A modem is similar to a transceiver, in that it sends and receives a signal, but a modem uses modulation and demodulation. It modulates a signal being transmitted and demodulates a signal being received.
Transceivers are called Medium Attachment Units (MAUs) in IEEE 802.3 documents, which were widely used in 10base2 and 10base5 Ethernet networks. Fibre-optic gigabit and 10 gigabit Ethernet utilize transceivers known as GBIC, SFP, XFP and XAUI.