Depth of field is the zone in a photo that appears acceptably sharp from front
to back. It controls how much of the scene is in focus and is one of the main tools photographers use to guide attention. A shallow depth of field means only a small part of the image is sharp, while the background and foreground blur softly. This is common in portraits, flower photos, and wildlife shots where you want the subject to stand out. A deep depth of field keeps much more of the scene sharp, which is useful for landscapes, architecture, and travel images.
Three main things affect depth of field: aperture, distance, and focal length. A wide aperture such as f/2.8 creates less depth of field. A smaller aperture such as f/11 creates more. The closer you are to your subject, the shallower the depth of field becomes. Longer lenses also tend to blur backgrounds more.
In simple terms, depth of field is not just about focus. It is about deciding what matters most in the frame and letting the viewer see it first.