A value indicating whether the geometry builder currently contains any curve segments. ArcGIS software supports polygon and polyline geometries that contain curve segments (where Segment.isCurve is true, sometimes known as true curves or nonlinear segments). Curves may be present in certain types of data - for example Mobile Map Packages (MMPKs), or geometry JSON.
From v100.12, you can use curves in a MultipartBuilder. New segment types CubicBezierSegment and EllipticArcSegment represent different types of curve that can be added to polygon and polyline geometries.