What's the difference between knots and fit points?

Question

For the spline curve, what's the difference between knots and fit points?

I know fit points are always on the curve, what does knots used for?

Answer 1

The fit points are the input data points. The knots are the limits between the various pieces of the spline.

They can coincide, for instance when you want to interpolate between points:

However, if you want a smooth curve that fits a noisy data curve, then you can use a spline with only a few knots (whose positions do not generally coincide with your data points):