Depth of Field (DOF) is the amount of your shot the will be in focus. Large depth of field means that most of your image will be in focus whether it's close to your camera or far away ( like a picture where the foreground and the background is largely in focus taken with an aperture of f 22). A small depth of field means that only part of the image will be in focus.
First Shoot
This photo has a empty depth of field effect for close up as the amuse background is thrown out of focus to draw the viewer's mind to the main subject.
This picture has a smaller aperture and it is used MAXIMUM depth of field to ensure all the elements are in focus.