oh, okay. I have never seen that tag been used for anything but roads and railways.
I'd still go with "barrier=retaining_wall" because the description matches exactly what a terrace is - a wall retaining the earth from sliding down. The flat ground is just a side-effect. I would expect an embankment to have one step and then have reached the highest level of whatever it intends to bank up. Also embankments usually have two sides, the one-sided being an exception.