buns of steel 

Danielle Steel's rock-hard buttix.

Danielle Steel must work those glutes, because she's got some seriously hot buns of steel!

buns of steel by NiraMillson September 13, 2016

buns of steel 

1. having a very tight rear end
2. having a butt that is so tight and toned, it is compared to steel

Tyler- Check out Lydian's behind, buns of steel, man!

Kelsea- Yeah dude...yeahhh...

buns of steel by Lydian Beck April 8, 2008