Mathematica Tutorial: Visualization And Graphics - Wolfram Research

Visualization and Graphics 73
If you give a list of graphics elements in two dimensions, Mathematica simply draws each
element in turn, with later elements obscuring earlier ones. In three dimensions, however,
Mathematica collects together all the graphics elements you specify, then displays them as
three-dimensional objects, with the ones in front in three-dimensional space obscuring those
behind.
In[5]:=
Every time you evaluate rantri, it generates a random triangle in three-dimensional space.
rantri := Polygon@Table@rcoord, 83