3D design is the process of creating physical or digital 3D models of any artifact. Physically this can be achieved using blocks such as Lego or with some playdough and some sticks.
Digitally, this is done through special applications that are build for 3D design purposes. Tinkercad is one example of such software.
3D design shows kids the relationship between art and STEM. It allows them to use their imagination and think outside the box.