What technique involves merging two or more 2D shapes into a unified 3D form?

The technique that involves merging two or more 2D shapes into a unified 3D form is commonly referred to as the union operation. This process allows for the combination of multiple geometric shapes into a single cohesive object by adding the volumes of the individual shapes together. When performing a union operation, the overlapping areas are merged, resulting in a new solid that encompasses the entirety of the original shapes.

In the context of 3D modeling and computer-aided design (CAD), the union operation plays a vital role in simplifying complex assemblies and ensuring that design components function as a single entity. This makes it especially useful in various design workflows, such as product design, architectural modeling, and engineering applications.

While other techniques like extruding, lofting, and filleting serve different purposes in shaping and refining 3D forms, they do not specifically emphasize the merging of multiple shapes into a single solid. Therefore, the union operation is the appropriate technique in this scenario for achieving a unified 3D structure from 2D shapes.