Spectrum

Spectrum is radio waves that are used to transmit data.  Radio waves are measured by wavelength and frequency with most communication networks operating between 300 MHz and 6 GHz frequency.

Licensed spectrum is used for private networks because there is a licensing fee which gives the user the exclusive right to transmit data on their assigned frequency without interference.

For private cellular networks, regulators have made mid-band spectrum in the 3.4-4.2 ghz range available.  This makes it the optimal frequency to operate large networks as it gives excellent square miles/kilometers of coverage and propagation without significant impacts from commonplace occlusions.