Ultrasonic Sensor Thingies

All educated (and not) peoples answer me!
It's about those Ultrasonic sensors.
Why are they called that. The stuff professionally called ultrasonic doesnt normally pass through air does it? I mean when examining metal parts for aircraft and stuff, and when examining body parts, they have to use gels and stuff for that purpose. I know for other purposes as well, but YOU DONT want air in the way...
So is it just a friendly way of saying higher pitched sound or something, like bat's radar and stuff?

I believe it is yes, just high frequency, inaudible to humans, sound. Ultrasonic sensor alarms generally use 40khz region sound, which is twice as high as what a good pair of human ears can hear

thanks

Ultrasonic is greater frequency than humans can hear.

Subsonic is lower frequency than humans can hear.

Subsonic can also mean a speed slower than the speed of sound.

therefore:-

Supersonic is a speed greater than the speed of sound.