Depth of field refers to the range of distance in a photo that appears sharp and in focus. A shallow depth of field means only a small part of the image is clear, while the background is blurred. This technique is often used in portrait photography to highlight the subject, like a person standing out against a soft, dreamy background. On the other hand, a deep depth of field keeps most of the scene in focus, which is ideal for landscapes or group shots. This allows details in both the foreground and background, such as mountains and trees, to be clearly visible, creating a more immersive experience.