Which of the following describes a G2 constraint?

A G2 constraint is specifically related to the geometric relationship between curves, particularly in the context of their tangential properties. When G2 is applied, it indicates that two curves not only touch each other but also have the same radius of curvature at the point of tangency, meaning they are smooth at that contact point. This relationship ensures that the curves flow together seamlessly without any abrupt changes in direction or curvature, which is critical in design scenarios where aesthetic and functional continuity is essential, such as in automotive or product design.

In contrast, the other answers describe different types of geometric relationships that do not match the criteria for a G2 constraint. For example, stating that objects are contiguous but not tangent does not satisfy the tangential requirement. Describing objects as parallel with a fixed distance apart indicates a linear relationship, which is not relevant to curvature. Lastly, defined angles of intersection relate to angular constraints rather than curvature. Therefore, the focus on tangency and equal curvature in the correct answer encapsulates the essence of a G2 constraint in geometrical relationships.