Definition:
Depth of field is the amount of distance between the nearest and farthest objects that appear in acceptably sharp focus in a photograph.
In other words, Depth of field means how much of the photograph is in focus and how much is blurred.
You will see in the photography below that there is a large depth of field. This means that most of the photograph is in focus.
Note particularly the blue bottle, the wine glasses and the chairs in the background.
The photography below has a shallow depth of field. This means that only a small part of the photograph is in focus and the rest is blurred.
Notice that the blue bottle is slightly blurry and that the chairs are very blurry. The right-hand wine glass has the sharpest focus.
Changing the depth of field can make your photographs more interesting.
A shallow depth of field will emphasise your subject. Look at how the yellow flower draws your attention.
Landscape photographs often need a large depth of field so the foreground and the background are in focus.
Look at the photograph below. The rail and the far hill are both in focus.
Compare the two Photographs below.
The first photograph has a large depth of field. You can clearly see the leaves and fence behind the flowers.
The second photograph has a shallow depth of field. The background is blurry and only the two flowers are emphasized.
Which of the above two photographs is better ? Well there is no right or wrong answer.
What you need to understand is how the depth of field changes the picture.
You need to be able to distinguish a shallow depth of field from a large depth of field.
This is clearly demonstrated in the two photographs above.