A simplified approach to rendering three-dimensional ('3D') environments that significantly reduces the computational burden. This is useful for interactive applications like video games and virtual tours that need to generate high frame rates. The classic first-person shooter DOOM is the canonical example of the form.
The approach essentially uses a static floor plan divided into individual geometric subregions. Visibility of each region is typically determined using a ray casting approach. Hidden surface removal (a.k.a. Z-buffer) is then used to determine the final visibility of each subregion.
There are some limitations to this approach, such as inability to cast shadows. It can also result in peculiar visual effects because every visible object is still really a 2D object, and thus only has one surface.