I often think about 3d graphics and make them all the time as fractals with Mandlebulber. (There are also 4d fractals.
Hypothetically a 4D fractal is our universe.)
3d or 2d?
The difference is that 3d graphics have x,y,z dimensions while the Gimp workspace is x and y. In Gimp you can map an object to a sphere or a box and then rotate it. Perceptually it's 3d because you can look at all sides of it but not at the same time. People are looking at 3d objects and 2d objects on a flat screen or as a flat image so 3d is often a perceptual illusion. Unless you 3d print your object. All video and pictures are the same. They are representations of what is 3d.
I have used Blender and agree with vittforlinux. It's 3d modelling that can make a physical object as true 3d but how often is it used for that?