There are several kinds of systems that do this. All of these systems include a single or multiple microphones that connect to some sort of central unit. The central unit controls the system and transmits the sound signal much like a radio station.
Infrared systems depend on a clear line of sight between the transmitter and the receiver.
If someone walks between them, or if a clear line of sight is not available, the infrared systems don't work. In this sense, they are more versatile. Because of these features and limitations, the FM systems tend to be the most versatile.