[pluma]

Technically it's a 2D surface extruded in real 3D space.

Early 3D games didn't have polygonal models and the levels were actually defined by a 2D grid (making it impossible to climb "on top" of something as each square could only be blocking or passable but had no "height"). Objects in the game world were drawn as 2D sprites on that 2D plane but it was all rendered in perspective to give the illusion of 3D.

Nowadays we call those games "2.5D" to distinguish them from modern 3D games which can render arbitrary polygonal objects.

This display is 2.5D. It basically "renders" a rectangular 2D texture with a low-resolution depth map by painting the texture on the screens and then extruding the screens according to the depth.