Depth of field is one area where photography gets science-y and hard to explain in a straightforward way, but I shall do my best. Depth of field is basically the distance between the nearest and furthest objects in a photograph that appear in focus. If you have a blurred background behind your subject, you shot with a shallow depth of field. If the background has the same focus as your subject, you shot with a deeper depth of field. Larger apertures (smaller f-stops) create a shallower depth of field and smaller ones create a deeper depth of field. At least as far as I know. It’s that pesky optical science part of photography that confuses me.