Is FM frequency in hertz, megahertz, or gigahertz?

I am wondering because I have an FM transmitter set at 88.3. Is that 88.3 hertz, mhz, or ghz. Thanks. Also I notice that when I come to the major cop spots on the interstate it sometimes disrupts the flow of music. Could the cop's radar gun have an effect on my fm transmitter? Thanks for the help.