"Triangle with Rounded Corners" ? I do not get it.
I think what he meant was the perimeter of the Triangle.
There is no such technical term as Circumference of a Triangle. There is however the Circumference of a Circle.
With all due respect Ancient Dragon, I think you should get your facts checked before berating someone, what with your stature here. It doesn't look good.
However if someone means the Perimeter of a Triangle , calling it the circumference would be incorrect.