Reverse roundhouse, I think that's what I know as an inverted kick ,or, inverted front kick. Used it alot in sparring and tournaments. Kinda like a front kick with the kicking leg turned knee out ;ie sideways, or a short upward angle round kick going across my body instead of with it, impacting with ball of the foot. Sound similar?
Another old post to reference...
In ITF tkd that sounds like a mid section twisting kick.
I've been told by people from 3 different schools (including mine) that they'd never seen anyone attempt to use it in sparring until I was their opponent.
Works very well actually - it's not a huge power kick but because it's utterly unexpected it knocks out wind every time
Edit: it's a kick present in karate too - Jesse Enkamp did a video on it.