A radio frequency band spanning 758 - 798 MHz, allocated by the FCC as part of an effort to help public safety agencies at all levels of government upgrade to newer and more interoperable radio systems throughout the United States.
The broader effort includes dedicated bands for both narrowband radio systems and broadband data. Band 14 covers the broadband data portion. The FCC has mandated LTE technology for band 14.
It's a paired band, meaning that 758 - 768 MHz is designated for network towers to transmit to mobile devices, while 788 - 798 MHz is for mobile devices to transmit to the network towers.
FirstNet is the government authority in charge of having a data network deployed in band 14. It has awarded a contract to AT&T for constructing and operating the network. In return, AT&T will be given part of the band to use commercially.