To main page
refers to the mesh
which has small (low) number of polygons.
Typically organic things, like trees, people, animals, require a lot of curved surfaces and since OpenGL thinks in triangles - we need a lot of very-very small triangles to create a believeable curved surface. It might be tens of millions of triangles needed to draw a single human, but average card can handle about a million
. And you need to show more than 1 person in game. Therefore there has been developed a number of tricks to develop a low polygon count models that look realistic.
Low poly from high poly
Typically you can model "high poly" object and then retopologize
it to "low poly" PLUS normal map
. That creates illusion
of additional faces, when in fact model stays low poly. The process is typically 3DS max/Maya/Blender -> Zbrush/Mudbox -> Topogun.
Alternative approach is to model low polygonal model and then adding details via DRAWING (in 2D app, like Photoshop) a normal map.