In optics, particularly as it relates to film and photography, the optical phenomenon known as depth of field, Is the distance about the plane of focus where objects appear acceptably sharp in an image.the zone of acceptable sharpness within a photo that will appear in focus. In every picture there is a certain area of your image in front of, and behind the subject that will appear in focus.It's not a fixed distance, it changes in size and can be described as either 'shallow' (where only a narrow zone appears sharp) or deep (where more of the picture appears sharp).Shallow depth of field enables you to blur background and foreground details, causing distractions to melt away and allowing you to direct viewers to the focal point in a picture.
Examples:
Shallow depth of field:
Deep depth of field:
Best image
Worst image
I think this is my best image because I have used a small aperture that has made the background go out of focus which is called shallow depth of field.
I think this is my worst image because the whole image is out of focus and there is no depth of field because everything is out of focus. The car and the background is blurred out and the exposure is a little bit light.