B-splines approximate a function using a series of polynomial patches. They are often used in computer graphics to create smooth curves between control points.
Used in Chap. 7: page 99
Links:
Wikipedia: B-spline
mathworld.wolfram.com: B-spline
cl.cam.ac.uk: Cambridge: B-splines

Example B-spline (source Wojciech mula, CC0, via Wikimedia Commons)