Depth of field is the range of focus in a shot. There are two ranges of this –

A “shallow focus” is when there is a small depth of field and only one part of the image is in focus while the rest is blurry. An example of this is used in the film “Fathers and Daughters”, where it focuses on Katie’s face and her reactions, so the audience is fully focusing on that rather than anything else in the background.

A “deep focus” uses a large depth of field, so the whole of the scene is in focus for the audience. An example of this is used in the film “Ex Machina”, and in this scene we can see other people in the background and what is going on around the humanoid.