Fillet

A fillet is a small, flat, usually narrow step or band separating two other elements of a profile -- a brief flat pause between two curves in a moulding profile, or the narrow flat land left between a chamfer and the rest of an edge, rather than letting the chamfer run directly into a sharp meeting line. It's a deliberate design detail, not a byproduct of an imprecise cut -- a fillet gives a profile a visual "rest," breaking up what would otherwise be one continuous curve or transition into a more considered, multi-part shape.