3D Solid Modelling
Solid modelling is where you create a representation of solid parts in 3D virtual space. The parts can then be viewed as if they were an actual manufactured product. This assures you that the parts are exactly as intended prior to prototyping and manufacture. The applications of solid modelling are wide ranging across many industries.
I use Sketchup Pro for modelling and also have experience in Autodesk Fusion 360 and Inventor.