Although NURBS curves are analytically generated, in order to generate and display them they must be approximated by line segments.
Curve approximation controls are displayed in the creation parameters for curve objects, and on a Curve Approximation rollout for NURBS models (top-level NURBS objects). At the model level, approximation controls affect all curve sub-objects in the model.
Curve approximation is accomplished by segments. One or more line segments, or steps, are used to approximate each segment of the curve. For point curves, a segment of a curve is the portion between one point and the next. For CV curves, the segment is determined by the CV’s parametric knot. The transition from one CV curve segment to another isn’t visible in viewports.
Curve approximation parameters aren't animatable.