Depth of Field

Depth of Field is the region of the scene that appears in focus.

A "shallow" depth of field means that a very narrow range of distances from the lens will appear in focus, while objects closer or farther away will appear out of focus. Shallow depth of field is very effective in portriat photography or any other situation where you do not want the background to distract the viewer's attention from the intended subject.

Conversely, a "deep" depth of field is effective for landscape photography where that sprig of grass or wildflower one foot from the lens is in focus, all the way to the mountain range background out at infinity.