5G is short hand for Fifth Generation. It is a data transmission protocol. You are using it right now on your phone.

It is radio. There are a lot of devices that use these frequencies. Two way radios like FRS, GMRS, MURS, DMRS, public safety, businesses, military, satellite, transponders, ADS-B, television, cellular, GPS, terrestrial fixed wireless internet, weather and aircraft radar, etc...

For a fixed Mount of power:

The higher the frequency the more data it can handle. The higher the frequency the less it can penentrate. At 2GHz even small trees interfere with data transmission. Lower frequencies carry less data but penetrate better. The phone in your hand produces upwards of 500mw of radio energy depending on how much is needed to reach the tower at minimum optimal power to send data reliably.

Radio frequencies authorized for 5G.

FR1, 410 MHz to 7125 MHz

FR2, 24.25 Ghz to 71.0 GHz

FR3, 7.125 GHz to 24.25 GHz