POV-Ray Geometric Shapes

triangle{ ...} - simple flat triangle shape

built-in shape, non-CSG

//Syntax: -----------------
triangle{ <vertex_1>,
          <vertex_2>,
          <vertex_3>
        } //---------------

Example:

// -------------------------------------------
triangle{ <0.0, 1.0,-1.0>,
          <0.0, 1.0, 2.0>,
          <1.0, 0.0, 1.0>
          texture{ pigment{ color rgb<0.5,1,0>}
                   finish { phong 1}
                 } // end of texture
          scale<1,1,1>
          rotate<0,0,0>
          translate<0,0,0>
        } // end of triangle -----------------

Note: "triangle" and "smooth_triangle" are used normally to build all those objects which are too complex to be made by built-in shapes. They are usually not created by hand but are converted from other files (i.e. files which use HF_macros with file output) or generated by utilities (i.e. POV_Tree + TOM_TREE for trees, Poser + converter PoseRay for human and animal creatures etc. )
See also: mesh and mesh2.