From FAS Virtual Worlds Almanac
A world has complex 3-D if it can support detailed, realistic, three dimensional objects and landscapes. The test for complex 3-d is whether or not a model of a human body can be created that looks realistic. To determine what is realistic, ask if a biology teacher could use the model of the human body in a classroom. Note that realistic does not necessarily mean photorealistic.
Support for complex 3-D: