TErrestrial Trunked Radio (formerly Terrestrial European Trunked Radio) is a radio communications in wide use around the world, although not in the United States. From Wikipedia’s entry “Terrestrial Trunked Radio.”

Terrestrial Trunked Radio (TETRA) (formerly known as Trans-European Trunked Radio) is a professional mobile radio and two-way transceiver (colloquially known as a walkie talkie) specification. TETRA was specifically designed for use by government agencies, emergency services, (police forces, fire departments, ambulance) for public safety networks, rail transportation staff for train radios, transport services and the military.

TETRA is an European Telecommunications Standards Institute (ETSI) standard, first version published 1995; it is mentioned by the European Radiocommunications Committee (ERC)