The us uses the US Customary Units system for normal day to day things, which we basically spackled our name on the more or less cloned Imperial System. “Imperial” is a much smaller mouthful than the actual name so unless you need to be very specific for some reason (like trying to aerobreak over mars….) we tend to just call it “imperial”, inherited from the British Empire.
The British don’t use it (much) anymore - the only countries I’m aware of that still use the Imperial System is Myanmar and Liberia. (But iirc, they’re planing on switching over and use metric along side. It’s been a while so they’ve probably switched,)
Scientific or technical things tend to use metric, and the military (or US geological service, that generates maps,) use metric