Depth of Field is what describes the amount of the image you can see.
A portrait of still photograph might use a Shallow Depth of Field to capture the main object and not the background. A Shallow Depth Of Field is where you can see the main part of the photograph and the rest of it is blurry. The image above is an example of a Shallow Depth of Field.
A Medium Depth Of Field is where you have the perfect image on one part of it and then the rest of it is slightly out of focus but you can still see what is in the background. It's visible but not perfectly clear. The image above shows this.
A Large Depth Of Field is where you can see the whole of the image with no blur. the image above is a Large Depth Of Field.