Pool pump wiring - 115v motor okay with L5-20 125V 20A Receptacle?
1) American house-current power is commonly described as anything from 110VAC to 120VAC.(Similarly, the higher voltage obtained by using both phases is called everything from 220VAC to 240VAC.) I believe this is mostly a historical artifact, and appliances labelled for anything in the respective range should work with any voltage within that range.

2) Fittings are overdesigned slightly for safety. So a receptacle intended for use with American house-current power will typically be rated for 125VAC. That doesn't mean it necessarily supplies 125VAC, only that it's tested and promised to be safe up to that (higher-than-needed) voltage.