You usually say 2.5D when it's a 3D but only from a single vantage point with no info of the back-facing side of objects. Like the representation you get from a

You usually say 2.5D when it's a 3D but only from a single vantage point with no info of the back-facing side of objects. Like the representation you get from a depth-sensor on a mobile phone, or when trying to extract depth from a single photo.