Wikipedia
A French curve is a template usually made from metal, wood or plastic composed of many different curves. It is used in manual drafting to draw smooth curves of varying radii. The shapes are segments of the Euler spiral or clothoid curve. The curve is placed on the drawing material, and a pencil, knife or other implement is traced around its curves to produce the desired result.
Usage examples of "french curve".
This had been laminated terrain to begin with, looking as if elevation contours had been artfully incised into the landscape, and the stream cuts revealed that the French curve laminae went down many meters, as if the map had marked the territory to a great depth.
They come so far up into the wind that the sail-mast spreads into a very taut French curve, and they lose way.
All the guys in the class were holding their French curve up at different angles, holding their pencil up to it at the lowest point and laying it along, and discovering that, sure enough, the tangent is horizontal.
The thing just to the right of the reference point looks something like a French curve, or maybe a paranoid sine wave.
Filling most of the room was a stylish French curve-shaped table equipped with a central display spine and surrounded by a dozen comfortable-looking chairs.