It's a digital radio (meaning, voice is transformed to ones and zeros, before the signal is put on the air) using TDM to make it possible for two simultanious c

It's a digital radio (meaning, voice is transformed to ones and zeros, before the signal is put on the air) using TDM to make it possible for two simultanious conversations to happen at the same time in the same place (by splitting the "time" into chunks - timeslots, so you get a few milliseconds to transmit and receive, and then you stay quiet and the other users using the other timeslot get to transmit and receive). It also adds some nice features such as groups and group calling, and since it's digital it's easy to route the data around and build cheap repeaters. It's used mostly by commercial services and ham radio operators.