General Mobile Radio Service, or GMRS radios, operate on specific UHF1 frequencies around 462 MHz and 467 MHz that are set aside by the FCC for general public use. UHF excels in transmitting through wooded environments, around town, or in any situation where there are obstructions when compared to other frequency ranges like VHF2. Because of this, GMRS is popular for overland, Jeep, camping, outdoor/adventure, and general recreational uses.
A valid FCC license is necessary to legally operate a GMRS radio. More info here
Access to the FCC Licence Manager here
