Which statement best describes a G2 constraint?

A G2 constraint, also known as curvature continuity, establishes a relationship between two curves or surfaces where they not only meet at a point but also share the same curvature at that point. This means that not only are the two objects tangent to each other, but they also have the same radius of curvature at the contact point. This ensures a smoother transition between the shapes, which is particularly important in applications like automotive and aerospace design where fluidity and aesthetics are crucial.

The other options provide different forms of geometric constraints but do not capture the specific essence of what a G2 constraint entails. For instance, having the same radius of curvature (as stated in the correct answer) fundamentally distinguishes a G2 constraint from merely being tangent or contiguous without considering curvature relationships. Thus, option B aptly reflects the nature of G2 constraints by emphasizing both tangency and curvature congruence.