What is 3D? 3D means Something that is 3 dimensional, something that has Height, Width and Depth. If the object doesn't have depth then it'll be 2D just like a paper. In computers, 3-D describes an image that provides the perception of depth. You can differentiate 3D by watching 2D videos on Youtube and watching a 3D video by in VR (Virtual Reality). Here it's a 3D scene but your seeing it as 2D because your eyes can see the depth of the video but you can't see what's left or right in the 3 dimension world. Here the video is 3D as well as the environment so that you can see in the 3D space in real time.