What are the shoes called that actually have a spherical ball underneath the sole of the shoe?

So I was on the Texas Tech University campus the other day, and I saw someone gliding around on these shoes, but each of them had about a 4-inch in diameter spherical ball underneath them. NOT to be confused with skate shoes or anything of the sort. What are these things!?

Heelies!!!!

hmmm not sure all ive herd of were some weird skethcers thing and heelys