Depleted uranium rounds are rounds with a small amount of uranium crammed in them, because the pointy metal thing that flew at you at 400 MPH wasn't dangerous enough.
It's not what these rounds do the human body that makes them terrifying though; it's what they do to armor. When depleted uranium rounds are in the hands of your enemy, the last place you'd want to be is inside of a tank.
This is because it's “self-sharpening,” which means when the round hits a hard target, it immediately hardens and burns through anything stupid enough to get in the way; the second it hits air, the round instantly catches fire and then explodes.
