A B-spline allows you to make a curved line with very few points. It has control points with equal weights to adjust the shape of the curve. The control points rarely reside on the curve itself, because the curve is an average of the points. For instance, if you make four control points in the shape of a square, the resulting curve will be a circle inside of that square, because the curve is pulled inward as it tries to average out the weights of all the four points. Different from bezier splines, which use control points that always touch the curve, and handles that help you adjust the curve.