(aka a radio station) is a communication device over a radio channel
(frequency), with direct and instantaneous communications. That's
why walkie-talkies are often used for guarding, for police, for
hunting, because they allow you to connect two subscribers in a couple
of seconds! 2 radios, each of which is both a receiver and a
transmitter (therefore they are called a receiving / transmitting
device), are tuned to the same frequency and alternately broadcast and
receive voice messages.