Is a descending curve when driving one where the radius of the curve gets smaller as you progress through it?

No, a descending curve typically refers to a curve where the road slopes downward, rather than one where the radius decreases. In driving terms, a descending curve can mean you're navigating a curve that leads downhill, but the radius can remain constant or even increase depending on the design of the road. A curve with a decreasing radius is referred to as a "tightening curve."