uh.....er....

technically speaking, all computer games are 2D, at least until someone invents a holographic projection system, at which time we will have 3D. until then, our "3d" is smoke and mirrors, cleverly rendering textured triangles onto the screen with a few extras to give the illusion of depth and light.

hehe - well i think that was a perfect answer
So i think by 3d he understood OpgenGL DirectX etc ...
Hui so Diablo is a 2D game , but Quake3 is a 3d game