This page has a perhaps more entertaining way to discuss surface continuity, but it also covers higher orders of continuity – G3 and G4.
If you’re curious to learn more about NURBS, I’m sharing a couple of links that go more in depth on how this geometry works.
This article links to a somewhat comprehensive definition of NURBS
This article links to two other that are more deep in their description, with equations and formulas that are quite complex:
The Wikipedia page for NURBS is also a useful reference: