The two terms related to the word "radius" in the context of discussing black holes are "Schwarzschild" and "AU."
The "Schwarzschild radius" refers to the radius of a black hole's event horizon, while "AU" (astronomical unit) is a unit of distance often used in astronomy, although it isn't specifically about black holes. The most relevant term here is "Schwarzschild" as it directly pertains to the radius concept in black hole physics.
So the answer is: Schwarzschild and AU.