A term you may see when programming or setting up your FM radio is "Wide Band" or "Narrow Band". Over the years this term has changed specifications.
Back in the late 50's and early 60's when two-way FM communications was in its infancy all transceivers were +/-15khz wide in deviation (modulation). Most were on the VHF-high band portion being 152-172 mhz. Pre 60's also used the VHF-low band portion from 30 to 50 mhz. The UHF band was late in coming and used the 450-470 mhz band. The VHF-H public service band was made up of police and fire communications as well as taxi cabs, public and private utilities. As more and more services were added to the mix the band was completely filled up and something had to be done. The F.C.C. ordered all radio communications equipment to cut the deviation down to +/-5khz and thus became "narrow band" and 15 khz radios were obsoleted if they weren't able to be modified to narrow band. In cutting the deviation more channels could be added.
An example of typical channel spacing would be 154.19 and 154.22 which is 30 khz channel spacing. With narrow banding a channel could be added between the two being 154.205 mhz. This virtually doubled the number of available channels. Up until the early 2000's this sufficed but still the channels filled up. The F.C.C. decided to split the channels again and half the deviation again down to 2.5 khz or 7.5 khz channel spacing. So between 154.19 and 154.205, 154.1975 mhz.
Since the old Wide Band was gone almost 40 years ago, the new "Wide Band" was the old "Narrow Band" and the new split is now the new "Narrow Band".
Many programmable hand held radios can be set for wide or narrow band operation. Sometime referred to W or N in the settings menu. You may also see an option for channel spacing or steps like 2.5, 5, 7.5, 10. These are only for manually setting the frequency from the front panel. These settings are unimportant if programming using software such as Chirp.
If you are on a given frequency and you are set to "wide" modulation and you are talking to someone that is set to "narrow", your audio may be too loud or it will distort or drop out. If you are set to "narrow" and you are talking to someone set to "wide", your audio may be low and almost unintelligible.
Remember, FRS radios are "narrow" and GMRS, MURS, and most ham radios are "wide" modulation.