A Fly Leg where fly line and leader are relatively free from curvature from Loop Nose to fly.

Related terms in Fly Leg Shapes: Convex Fly Leg, Concave Fly Leg, Trailing Loop, Tailing Loop, Under-Running Loop, In-Plane Loop

From the FFI Fly Casting Definitions (2025 Edition), reproduced with attribution to Fly Fishers International.