FRS stands for Family Radio Service.
MRS is more correctly known as GMRS.
GMRS stands for General Mobile Radio Service.
FRS and GMRS both share some channels, but their purposes are slightly different.
Some differences between FRS and GMRS are:
1. FRS does not require an FCC license; GMRS requires a $75 license.
2. FRS radios are limited to .5 watts; GMRS radios can transmit at up to 50 watts.
3. Repeaters are not allowed on FRS; Repeaters are allowed on GMRS.