re:
> about translation (language) what exactly "span" in the text above ?
It's basically a section of a curve that can be directly evaluated as a polynomial function (as a Bezier).
When you have a curve or surface that has a lot of points in it, it's not practical to use a single polynomial to evaluate the whole thing so there needs to be a way to chain together several of them. Part of how NURBS curves work is that it defines how these spans share points with each other so they can automatically stay smooth to each other.
Les mots qui me sembleraient les plus proches du sens de span dans ce contexte seraient : la "portée", "l'étendue" ou la "couverture".
Lequel serait le plus précis ?