Citizens' band uses a certain radio frequency to enable users to talk to each other over short distances.
They are about the size of a car radio with a handheld microphone. Quite a cumbersome machine compared to today's communication devices.
I've used them where cell phones won't go. Its just a radio transceiver designed to run on frequencies allocated for citizen's use. Check out en.wikipedia.org/wiki/Convoy_(song). Nobody uses those terms anymore. We mostly use it here in the states in commercial trucks to keep awake and find out where the law is hiding. Very few people use call signs or any of that stuff anymore.