Here is what I learned about focus: focus is weather your image is sharp or blurry. A sharp subject would be an in-focus subject. A blurry subject is an out-of-focus subject. You can use your aperture to control depth of field, which is how much of your background and foreground are in focus. If you are doing a landscape photo, use a sharper focus on your landscape, rather than your midground or foreground. While shooting portraits, use a sharp focus on your person, and you may or may not want a blurry background and foreground.