Depth of Field (DoF)

Depth of field, or DoF, is the range of distances within the frame that are in focus.
Depth of field is determined by the f-stop value.
Lenses that allow for a shallow depth of field are 50mm f/1.8 

Deep Depth of Field

A smaller aperture (larger f-stop value) has a deeper depth of field. These f-stop values are good for landscape shots or other scenes in which you want things in the foreground and the background to be in focus.

Deep Depth of Field Example

Shallow Depth of Field

A larger aperture (smaller f-stop value) has a shallower depth of field. These f-stop values are good for macro shots or other scenes in which you want a specific area to be in focus with things in the foreground and/or background to be out of focus.

Shallow Depth of Field Example