By definition: DOF
In optics, particularly as it relates to film and photography, depth of field (DOF) is the distance between the nearest and farthest objects in a scene that appear acceptably sharp in an image. Although a lens can precisely focus at only one distance at a time, the decrease in sharpness is gradual on each side of the focused distance, so that within the DOF, the unsharpness is imperceptible under normal viewing conditions.
A visible scene, especially one extending to a distance.(Classic example is looking down railroad tracks that seem to come to a point, knowing they never do).
Its important not to confuse the two. In the examples, you can see the impact of DOF in clear, sharpness of the last glass object . Oppositely you can see the distance in the roadway image but it gradually gets harder to see the image clearly and seems to go on forever.