First off, the FCC has allocated different frequencies to different activities in the U.S. For example, cell phones have their own assigned frequencies, baby monitors have their own frequencies, CB radios have their own, and so on.
FM radio stations all transmit in a band between 88 megahertz (millions of cycles per second) and 108 megahertz.
This band of frequencies is completely arbitrary and is based, frankly, mostly on history and whim - it doesn't *have* to be that way, but it is, and it works, so it probably won't be changed. Inside that band, each station occupies a 200 kilohertz slice, and all of the slices start on odd number boundaries. So there can be a station at 88.1 megahertz, 88.3 megahertz, 88.5 megahertz, and so on.
The 200 kilohertz spacing, and the fact that they all on odd
boundaries is, once again, completely arbitrary and was decided by the FCC. For example, in Europe the FM stations
are spaced 100 kilohertz apart instead of 200 kilohertz apart, and they can be even or odd. Neither way is right or wrong, so long as everybody follows the same rules in a given area. As to not following the rules - that way lies chaos.
The Motown female group The Supremes, which dominated the pop charts in the 1960's, was originally called The Primettes.
