Inversion ??

So I'm 36 weeks and baby is still breech. I have another ultrasound scheduled in a week & if he's still breech, they want to do an inversion the following day. She said something like they're going to do a spinal and an inversion or maybe it was "a spinal inversion", I have no idea. I should've asked her to explain but I was in a bit of a hurry, so I didn't think to. Anyone know what it could be? I know it's to get baby to flip, but what should I expect??