Depth of field

Depth of field refers to the focal length.

Deep Focus 

Deep focus is when the frame shows you everything in focus or sharp this is called Deep focus.It  requires a small aperture and lots of light , this means that the foreground, middleground and background of the frame remain in focus.

Shallow Focus

Shallow focus is a function of a narrow depth of field and it implies that only one plane of the frame will remain sharp and clear, the rest of it is blurred  (usually the foreground).