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 108
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)