Depth of field (DOF) refers to how much of a photo is sharp in front and back of where you focus on the main subject. DOF is primarily controlled by aperture size though other factors come into play such as the focal length of the lens and the distance the background is from the subject.
Photographers may consciously control depth of field for artistic purposes, aiming to achieve attractive background blur known as bokeh. For example, a shallow depth of field is often used when taking close up shots so the background is blurred and the main subject is in sharp focus.
More (deep) DOF
Photo with deep depth of field
Deep depth of field means that all or most of the picture is in focus from front to back. It is often used for capturing subjects in the distance, such as in landscape scenes.
The further away your camera is from the subject, the greater the depth of field.
Less (shallow) DOF
Photo with shallow depth of field
Less depth of field means that a subject is in focus but objects in front and behind it appear out of focus. Less DOF is often desired when taking portrait, close-up and macro shots.
Lower f-stops (larger apertures) decrease DOF. Long focal lengths (zooming in) produce less DOF.
You can also make the background appear out of focus by placing the subject close to the camera and having the background far away.
If you can’t manually control aperture, use Portrait or Macro mode for shallow depth of field. For deep depth of field, use Landscape or Infinity mode.